commit 173a95b19f676fe93b52f7e9a5a3461b36da3ceb
Author: 左程云 <zuochengyun@zuochengyundeMacBook-Pro.local>
Date:   Tue Apr 28 18:26:54 2020 +0800

    first commit

diff --git a/src/class01/Code01_SelectionSort.java b/src/class01/Code01_SelectionSort.java
new file mode 100644
index 0000000..8bd4c27
--- /dev/null
+++ b/src/class01/Code01_SelectionSort.java
@@ -0,0 +1,116 @@
+package class01;
+
+import java.util.Arrays;
+
+public class Code01_SelectionSort {
+
+	public static void selectionSort(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return;
+		}
+		// 0 ~ N-1
+		// 1~n-1
+		// 2
+		for (int i = 0; i < arr.length - 1; i++) { // i ~ N-1
+			// 最小值在哪个位置上  i～n-1
+			int minIndex = i;
+			for (int j = i + 1; j < arr.length; j++) { // i ~ N-1 上找最小值的下标 
+				minIndex = arr[j] < arr[minIndex] ? j : minIndex;
+			}
+			swap(arr, i, minIndex);
+		}
+	}
+
+	public static void swap(int[] arr, int i, int j) {
+		int tmp = arr[i];
+		arr[i] = arr[j];
+		arr[j] = tmp;
+	}
+
+	// for test
+	public static void comparator(int[] arr) {
+		Arrays.sort(arr);
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		// Math.random()   [0,1)  
+		// Math.random() * N  [0,N)
+		// (int)(Math.random() * N)  [0, N-1]
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			// [-? , +?]
+			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[] copyArray(int[] arr) {
+		if (arr == null) {
+			return null;
+		}
+		int[] res = new int[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			res[i] = arr[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static boolean isEqual(int[] arr1, int[] arr2) {
+		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
+			return false;
+		}
+		if (arr1 == null && arr2 == null) {
+			return true;
+		}
+		if (arr1.length != arr2.length) {
+			return false;
+		}
+		for (int i = 0; i < arr1.length; i++) {
+			if (arr1[i] != arr2[i]) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	// for test
+	public static void main(String[] args) {
+		int testTime = 500000;
+		int maxSize = 100;
+		int maxValue = 100;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr1 = generateRandomArray(maxSize, maxValue);
+			int[] arr2 = copyArray(arr1);
+			selectionSort(arr1);
+			comparator(arr2);
+			if (!isEqual(arr1, arr2)) {
+				succeed = false;
+				printArray(arr1);
+				printArray(arr2);
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Fucking fucked!");
+
+		int[] arr = generateRandomArray(maxSize, maxValue);
+		printArray(arr);
+		selectionSort(arr);
+		printArray(arr);
+	}
+
+}
diff --git a/src/class01/Code02_BubbleSort.java b/src/class01/Code02_BubbleSort.java
new file mode 100644
index 0000000..14b6e47
--- /dev/null
+++ b/src/class01/Code02_BubbleSort.java
@@ -0,0 +1,110 @@
+package class01;
+
+import java.util.Arrays;
+
+public class Code02_BubbleSort {
+
+	public static void bubbleSort(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return;
+		}
+		// 0 ~ N-1
+		// 0 ~ N-2
+		// 0 ~ N-3
+		for (int e = arr.length - 1; e > 0; e--) { // 0 ~ e
+			for (int i = 0; i < e; i++) {
+				if (arr[i] > arr[i + 1]) {
+					swap(arr, i, i + 1);
+				}
+			}
+		}
+	}
+
+	// 交换arr的i和j位置上的值
+	public static void swap(int[] arr, int i, int j) {
+		arr[i] = arr[i] ^ arr[j];
+		arr[j] = arr[i] ^ arr[j];
+		arr[i] = arr[i] ^ arr[j];
+	}
+
+	// for test
+	public static void comparator(int[] arr) {
+		Arrays.sort(arr);
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[] copyArray(int[] arr) {
+		if (arr == null) {
+			return null;
+		}
+		int[] res = new int[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			res[i] = arr[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static boolean isEqual(int[] arr1, int[] arr2) {
+		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
+			return false;
+		}
+		if (arr1 == null && arr2 == null) {
+			return true;
+		}
+		if (arr1.length != arr2.length) {
+			return false;
+		}
+		for (int i = 0; i < arr1.length; i++) {
+			if (arr1[i] != arr2[i]) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	// for test
+	public static void main(String[] args) {		
+		int testTime = 500000;
+		int maxSize = 100;
+		int maxValue = 100;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr1 = generateRandomArray(maxSize, maxValue);
+			int[] arr2 = copyArray(arr1);
+			bubbleSort(arr1);
+			comparator(arr2);
+			if (!isEqual(arr1, arr2)) {
+				succeed = false;
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Fucking fucked!");
+
+		int[] arr = generateRandomArray(maxSize, maxValue);
+		printArray(arr);
+		bubbleSort(arr);
+		printArray(arr);
+	}
+
+}
diff --git a/src/class01/Code03_InsertionSort.java b/src/class01/Code03_InsertionSort.java
new file mode 100644
index 0000000..79861c9
--- /dev/null
+++ b/src/class01/Code03_InsertionSort.java
@@ -0,0 +1,113 @@
+package class01;
+
+import java.util.Arrays;
+
+public class Code03_InsertionSort {
+
+	public static void insertionSort(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return;
+		}
+		// 0~0 有序的
+		// 0~i 想有序
+		for (int i = 1; i < arr.length; i++) { // 0 ~ i 做到有序
+			for (int j = i - 1; j >= 0 && arr[j] > arr[j + 1]; j--) {
+				swap(arr, j, j + 1);
+			}
+		}
+	}
+
+	// i和j是一个位置的话，会出错
+	public static void swap(int[] arr, int i, int j) {
+		arr[i] = arr[i] ^ arr[j];
+		arr[j] = arr[i] ^ arr[j];
+		arr[i] = arr[i] ^ arr[j];
+	}
+
+	// for test
+	public static void comparator(int[] arr) {
+		Arrays.sort(arr);
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		// Math.random() ->  [0,1) 所有的小数，等概率返回一个
+		// Math.random() * N -> [0,N) 所有小数，等概率返回一个
+		// (int)(Math.random() * N) -> [0,N-1] 所有的整数，等概率返回一个
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())]; // 长度随机 
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random()) 
+					- (int) (maxValue * Math.random());
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[] copyArray(int[] arr) {
+		if (arr == null) {
+			return null;
+		}
+		int[] res = new int[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			res[i] = arr[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static boolean isEqual(int[] arr1, int[] arr2) {
+		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
+			return false;
+		}
+		if (arr1 == null && arr2 == null) {
+			return true;
+		}
+		if (arr1.length != arr2.length) {
+			return false;
+		}
+		for (int i = 0; i < arr1.length; i++) {
+			if (arr1[i] != arr2[i]) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	// for test
+	public static void main(String[] args) {
+		int testTime = 500000;
+		int maxSize = 100; // 随机数组的长度0～100
+		int maxValue = 100;// 值：-100～100
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr1 = generateRandomArray(maxSize, maxValue);
+			int[] arr2 = copyArray(arr1);
+			insertionSort(arr1);
+			comparator(arr2);
+			if (!isEqual(arr1, arr2)) {
+				// 打印arr1
+				// 打印arr2
+				succeed = false;
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Fucking fucked!");
+
+		int[] arr = generateRandomArray(maxSize, maxValue);
+		printArray(arr);
+		insertionSort(arr);
+		printArray(arr);
+	}
+
+}
diff --git a/src/class01/Code04_BSExist.java b/src/class01/Code04_BSExist.java
new file mode 100644
index 0000000..9010182
--- /dev/null
+++ b/src/class01/Code04_BSExist.java
@@ -0,0 +1,30 @@
+package class01;
+
+public class Code04_BSExist {
+
+	public static boolean exist(int[] sortedArr, int num) {
+		if (sortedArr == null || sortedArr.length == 0) {
+			return false;
+		}
+		int L = 0;
+		int R = sortedArr.length - 1;
+		int mid = 0;
+		// L..R
+		while (L < R) {
+			// mid = (L+R) / 2;
+			// L 10亿  R 18亿
+			// mid = L + (R - L) / 2
+			// N / 2    N >> 1
+			mid = L + ((R - L) >> 1); // mid = (L + R) / 2
+			if (sortedArr[mid] == num) {
+				return true;
+			} else if (sortedArr[mid] > num) {
+				R = mid - 1;
+			} else {
+				L = mid + 1;
+			}
+		}
+		return sortedArr[L] == num;
+	}
+
+}
diff --git a/src/class01/Code05_BSNearLeft.java b/src/class01/Code05_BSNearLeft.java
new file mode 100644
index 0000000..6737501
--- /dev/null
+++ b/src/class01/Code05_BSNearLeft.java
@@ -0,0 +1,75 @@
+package class01;
+
+import java.util.Arrays;
+
+public class Code05_BSNearLeft {
+
+	// 在arr上，找满足>=value的最左位置
+	public static int nearestIndex(int[] arr, int value) {
+		int L = 0;
+		int R = arr.length - 1;
+		int index = -1; // 记录最左的对号
+		while (L <= R) {
+			int mid = L + ((R - L) >> 1);
+			if (arr[mid] >= value) {
+				index = mid;
+				R = mid - 1;
+			} else {
+				L = mid + 1;
+			}
+		}
+		return index;
+	}
+
+	// for test
+	public static int test(int[] arr, int value) {
+		for (int i = 0; i < arr.length; i++) {
+			if (arr[i] >= value) {
+				return i;
+			}
+		}
+		return -1;
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+		}
+		return arr;
+	}
+	
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	public static void main(String[] args) {
+		int testTime = 500000;
+		int maxSize = 10;
+		int maxValue = 100;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr = generateRandomArray(maxSize, maxValue);
+			Arrays.sort(arr);
+			int value = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+			if (test(arr, value) != nearestIndex(arr, value)) {
+				printArray(arr);
+				System.out.println(value);
+				System.out.println(test(arr, value));
+				System.out.println(nearestIndex(arr, value));
+				succeed = false;
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Fucking fucked!");
+	}
+
+}
diff --git a/src/class01/Code05_BSNearRight.java b/src/class01/Code05_BSNearRight.java
new file mode 100644
index 0000000..f3b6f25
--- /dev/null
+++ b/src/class01/Code05_BSNearRight.java
@@ -0,0 +1,75 @@
+package class01;
+
+import java.util.Arrays;
+
+public class Code05_BSNearRight {
+
+	// 在arr上，找满足<=value的最右位置
+	public static int nearestIndex(int[] arr, int value) {
+		int L = 0;
+		int R = arr.length - 1;
+		int index = -1; // 记录最右的对号
+		while (L <= R) {
+			int mid = L + ((R - L) >> 1);
+			if (arr[mid] <= value) {
+				index = mid;
+				L = mid + 1;
+			} else {
+				R = mid - 1;
+			}
+		}
+		return index;
+	}
+
+	// for test
+	public static int test(int[] arr, int value) {
+		for (int i = arr.length - 1; i >= 0; i--) {
+			if (arr[i] <= value) {
+				return i;
+			}
+		}
+		return -1;
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+		}
+		return arr;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	public static void main(String[] args) {
+		int testTime = 500000;
+		int maxSize = 10;
+		int maxValue = 100;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr = generateRandomArray(maxSize, maxValue);
+			Arrays.sort(arr);
+			int value = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+			if (test(arr, value) != nearestIndex(arr, value)) {
+				printArray(arr);
+				System.out.println(value);
+				System.out.println(test(arr, value));
+				System.out.println(nearestIndex(arr, value));
+				succeed = false;
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Fucking fucked!");
+	}
+
+}
diff --git a/src/class01/Code06_BSAwesome.java b/src/class01/Code06_BSAwesome.java
new file mode 100644
index 0000000..bdca00d
--- /dev/null
+++ b/src/class01/Code06_BSAwesome.java
@@ -0,0 +1,31 @@
+package class01;
+
+public class Code06_BSAwesome {
+
+	public static int getLessIndex(int[] arr) {
+		if (arr == null || arr.length == 0) {
+			return -1; // no exist
+		}
+		if (arr.length == 1 || arr[0] < arr[1]) {
+			return 0;
+		}
+		if (arr[arr.length - 1] < arr[arr.length - 2]) {
+			return arr.length - 1;
+		}
+		int left = 1;
+		int right = arr.length - 2;
+		int mid = 0;
+		while (left < right) {
+			mid = (left + right) / 2;
+			if (arr[mid] > arr[mid - 1]) {
+				right = mid - 1;
+			} else if (arr[mid] > arr[mid + 1]) {
+				left = mid + 1;
+			} else {
+				return mid;
+			}
+		}
+		return left;
+	}
+
+}
diff --git a/src/class01/Code07_EvenTimesOddTimes.java b/src/class01/Code07_EvenTimesOddTimes.java
new file mode 100644
index 0000000..d9e9327
--- /dev/null
+++ b/src/class01/Code07_EvenTimesOddTimes.java
@@ -0,0 +1,81 @@
+package class01;
+
+public class Code07_EvenTimesOddTimes {
+
+	// arr中，只有一种数，出现奇数次
+	public static void printOddTimesNum1(int[] arr) {
+		int eor = 0;
+		for (int i = 0; i < arr.length; i++) {
+			eor ^= arr[i];
+		}
+		System.out.println(eor);
+	}
+
+	// arr中，有两种数，出现奇数次
+	public static void printOddTimesNum2(int[] arr) {
+		int eor = 0;
+		for (int i = 0; i < arr.length; i++) {
+			eor ^= arr[i];
+		}
+		// eor = a ^ b
+		// eor != 0
+		// eor必然有一个位置上是1
+		// 0110010000
+		// 0000010000
+		int rightOne = eor & (~eor + 1); // 提取出最右的1
+		int onlyOne = 0; // eor'
+		for (int i = 0 ; i < arr.length;i++) {
+			//  arr[1] =  111100011110000
+			// rightOne=  000000000010000
+			if ((arr[i] & rightOne) != 0) {
+				onlyOne ^= arr[i];
+			}
+		}
+		System.out.println(onlyOne + " " + (eor ^ onlyOne));
+	}
+
+	
+	public static int bit1counts(int N) {
+		int count = 0;
+		
+		//   011011010000
+		//   000000010000     1
+		
+		//   011011000000
+		// 
+		
+		
+		
+		while(N != 0) {
+			int rightOne = N & ((~N) + 1);
+			count++;
+			N ^= rightOne;
+			// N -= rightOne
+		}
+		
+		
+		return count;
+		
+	}
+	
+	
+	public static void main(String[] args) {
+		int a = 5;
+		int b = 7;
+
+		a = a ^ b;
+		b = a ^ b;
+		a = a ^ b;
+
+		System.out.println(a);
+		System.out.println(b);
+
+		int[] arr1 = { 3, 3, 2, 3, 1, 1, 1, 3, 1, 1, 1 };
+		printOddTimesNum1(arr1);
+
+		int[] arr2 = { 4, 3, 4, 2, 2, 2, 4, 1, 1, 1, 3, 3, 1, 1, 1, 4, 2, 2 };
+		printOddTimesNum2(arr2);
+
+	}
+
+}
diff --git a/src/class01/Test.java b/src/class01/Test.java
new file mode 100644
index 0000000..af227e6
--- /dev/null
+++ b/src/class01/Test.java
@@ -0,0 +1,45 @@
+package class01;
+
+public class Test {
+	
+	public static void main(String[] args) {
+		int a = 6;
+		int b = 6;
+		
+		
+		a = a ^ b;
+		b = a ^ b;
+		a = a ^ b;
+		
+		
+		System.out.println(a);
+		System.out.println(b);
+		
+		
+		
+		
+		int[] arr = {3,1,100};
+		
+		System.out.println(arr[0]);
+		System.out.println(arr[2]);
+		
+		swap(arr, 0, 0);
+		
+		System.out.println(arr[0]);
+		System.out.println(arr[2]);
+		
+		
+		
+	}
+	
+	
+	public static void swap (int[] arr, int i, int j) {
+		// arr[0] = arr[0] ^ arr[0];
+		arr[i]  = arr[i] ^ arr[j];
+		arr[j]  = arr[i] ^ arr[j];
+		arr[i]  = arr[i] ^ arr[j];
+	}
+	
+	
+
+}
diff --git a/src/class02/Code01_ReverseList.java b/src/class02/Code01_ReverseList.java
new file mode 100644
index 0000000..d44df68
--- /dev/null
+++ b/src/class02/Code01_ReverseList.java
@@ -0,0 +1,198 @@
+package class02;
+
+import java.util.ArrayList;
+
+public class Code01_ReverseList {
+
+	public static class Node {
+		public int value;
+		public Node next;
+
+		public Node(int data) {
+			value = data;
+		}
+	}
+
+	public static class DoubleNode {
+		public int value;
+		public DoubleNode last;
+		public DoubleNode next;
+
+		public DoubleNode(int data) {
+			value = data;
+		}
+	}
+
+	public static Node reverseLinkedList(Node head) {
+		Node pre = null;
+		Node next = null;
+		while (head != null) {
+			next = head.next;
+			head.next = pre;
+			pre = head;
+			head = next;
+		}
+		return pre;
+	}
+
+	public static DoubleNode reverseDoubleList(DoubleNode head) {
+		DoubleNode pre = null;
+		DoubleNode next = null;
+		while (head != null) {
+			next = head.next;
+			head.next = pre;
+			head.last = next;
+			pre = head;
+			head = next;
+		}
+		return pre;
+	}
+
+	public static Node testReverseLinkedList(Node head) {
+		if (head == null) {
+			return null;
+		}
+		ArrayList<Node> list = new ArrayList<>();
+		while (head != null) {
+			list.add(head);
+			head = head.next;
+		}
+		list.get(0).next = null;
+		int N = list.size();
+		for (int i = 1; i < N; i++) {
+			list.get(i).next = list.get(i - 1);
+		}
+		return list.get(N - 1);
+	}
+
+	public static DoubleNode testReverseDoubleList(DoubleNode head) {
+		if (head == null) {
+			return null;
+		}
+		ArrayList<DoubleNode> list = new ArrayList<>();
+		while (head != null) {
+			list.add(head);
+			head = head.next;
+		}
+		list.get(0).next = null;
+		DoubleNode pre = list.get(0);
+		int N = list.size();
+		for (int i = 1; i < N; i++) {
+			DoubleNode cur = list.get(i);
+			cur.last = null;
+			cur.next = pre;
+			pre.last = cur;
+			pre = cur;
+		}
+		return list.get(N - 1);
+	}
+
+	public static Node generateRandomLinkedList(int len, int value) {
+		int size = (int) (Math.random() * (len + 1));
+		if (size == 0) {
+			return null;
+		}
+		size--;
+		Node head = new Node((int) (Math.random() * (value + 1)));
+		Node pre = head;
+		while (size != 0) {
+			Node cur = new Node((int) (Math.random() * (value + 1)));
+			pre.next = cur;
+			pre = cur;
+			size--;
+		}
+		return head;
+	}
+
+	public static DoubleNode generateRandomDoubleList(int len, int value) {
+		int size = (int) (Math.random() * (len + 1));
+		if (size == 0) {
+			return null;
+		}
+		size--;
+		DoubleNode head = new DoubleNode((int) (Math.random() * (value + 1)));
+		DoubleNode pre = head;
+		while (size != 0) {
+			DoubleNode cur = new DoubleNode((int) (Math.random() * (value + 1)));
+			pre.next = cur;
+			cur.last = pre;
+			pre = cur;
+			size--;
+		}
+		return head;
+	}
+
+	// 要求无环，有环别用这个函数
+	public static boolean checkLinkedListEqual(Node head1, Node head2) {
+		while (head1 != null && head2 != null) {
+			if (head1.value != head2.value) {
+				return false;
+			}
+			head1 = head1.next;
+			head2 = head2.next;
+		}
+		return head1 == null && head2 == null;
+	}
+
+	// 要求无环，有环别用这个函数
+	public static boolean checkDoubleListEqual(DoubleNode head1, DoubleNode head2) {
+		boolean null1 = head1 == null;
+		boolean null2 = head2 == null;
+		if (null1 && null2) {
+			return true;
+		}
+		if (null1 ^ null2) {
+			return false;
+		}
+		if (head1.last != null || head2.last != null) {
+			return false;
+		}
+		DoubleNode end1 = null;
+		DoubleNode end2 = null;
+		while (head1 != null && head2 != null) {
+			if (head1.value != head2.value) {
+				return false;
+			}
+			end1 = head1;
+			end2 = head2;
+			head1 = head1.next;
+			head2 = head2.next;
+		}
+		if (head1 != null || head2 != null) {
+			return false;
+		}
+		while (end1 != null && end2 != null) {
+			if (end1.value != end2.value) {
+				return false;
+			}
+			end1 = end1.last;
+			end2 = end2.last;
+		}
+		return end1 == null && end2 == null;
+	}
+
+	public static void main(String[] args) {
+		int len = 50;
+		int value = 100;
+		int testTime = 100000;
+		for (int i = 0; i < testTime; i++) {
+			Node node1 = generateRandomLinkedList(len, value);
+			Node reverse1 = reverseLinkedList(node1);
+			Node back1 = testReverseLinkedList(reverse1);
+			if (!checkLinkedListEqual(node1, back1)) {
+				System.out.println("oops!");
+				break;
+			}
+			DoubleNode node2 = generateRandomDoubleList(len, value);
+			DoubleNode reverse2 = reverseDoubleList(node2);
+			DoubleNode back2 = testReverseDoubleList(reverse2);
+			if (!checkDoubleListEqual(node2, back2)) {
+				System.out.println("oops!");
+				break;
+			}
+		}
+		System.out.println("finish!");
+
+	}
+
+}
diff --git a/src/class02/Code02_DeleteGivenValue.java b/src/class02/Code02_DeleteGivenValue.java
new file mode 100644
index 0000000..45f3008
--- /dev/null
+++ b/src/class02/Code02_DeleteGivenValue.java
@@ -0,0 +1,36 @@
+package class02;
+
+public class Code02_DeleteGivenValue {
+
+	public static class Node {
+		public int value;
+		public Node next;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static Node removeValue(Node head, int num) {
+		while (head != null) {
+			if (head.value != num) {
+				break;
+			}
+			head = head.next;
+		}
+		// head来到 第一个不需要删的位置
+		Node pre = head;
+		Node cur = head;
+		// 
+		while (cur != null) {
+			if (cur.value == num) {
+				pre.next = cur.next;
+			} else {
+				pre = cur;
+			}
+			cur = cur.next;
+		}
+		return head;
+	}
+
+}
diff --git a/src/class02/Code03_DoubleEndsQueueToStackAndQueue.java b/src/class02/Code03_DoubleEndsQueueToStackAndQueue.java
new file mode 100644
index 0000000..989096a
--- /dev/null
+++ b/src/class02/Code03_DoubleEndsQueueToStackAndQueue.java
@@ -0,0 +1,183 @@
+package class02;
+
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.Stack;
+
+public class Code03_DoubleEndsQueueToStackAndQueue {
+
+	public static class Node<T> {
+		public T value;
+		public Node<T> last;
+		public Node<T> next;
+
+		public Node(T data) {
+			value = data;
+		}
+	}
+
+	public static class DoubleEndsQueue<T> {
+		public Node<T> head;
+		public Node<T> tail;
+
+		public void addFromHead(T value) {
+			Node<T> cur = new Node<T>(value);
+			if (head == null) {
+				head = cur;
+				tail = cur;
+			} else {
+				cur.next = head;
+				head.last = cur;
+				head = cur;
+			}
+		}
+
+		public void addFromBottom(T value) {
+			Node<T> cur = new Node<T>(value);
+			if (head == null) {
+				head = cur;
+				tail = cur;
+			} else {
+				cur.last = tail;
+				tail.next = cur;
+				tail = cur;
+			}
+		}
+
+		public T popFromHead() {
+			if (head == null) {
+				return null;
+			}
+			Node<T> cur = head;
+			if (head == tail) {
+				head = null;
+				tail = null;
+			} else {
+				head = head.next;
+				cur.next = null;
+				head.last = null;
+			}
+			return cur.value;
+		}
+
+		public T popFromBottom() {
+			if (head == null) {
+				return null;
+			}
+			Node<T> cur = tail;
+			if (head == tail) {
+				head = null;
+				tail = null;
+			} else {
+				tail = tail.last;
+				tail.next = null;
+				cur.last = null;
+			}
+			return cur.value;
+		}
+
+		public boolean isEmpty() {
+			return head == null;
+		}
+
+	}
+
+	public static class MyStack<T> {
+		private DoubleEndsQueue<T> queue;
+
+		public MyStack() {
+			queue = new DoubleEndsQueue<T>();
+		}
+
+		public void push(T value) {
+			queue.addFromHead(value);
+		}
+
+		public T pop() {
+			return queue.popFromHead();
+		}
+
+		public boolean isEmpty() {
+			return queue.isEmpty();
+		}
+
+	}
+
+	public static class MyQueue<T> {
+		private DoubleEndsQueue<T> queue;
+
+		public MyQueue() {
+			queue = new DoubleEndsQueue<T>();
+		}
+
+		public void push(T value) {
+			queue.addFromHead(value);
+		}
+
+		public T poll() {
+			return queue.popFromBottom();
+		}
+
+		public boolean isEmpty() {
+			return queue.isEmpty();
+		}
+
+	}
+
+	public static boolean isEqual(Integer o1, Integer o2) {
+		if (o1 == null && o2 != null) {
+			return false;
+		}
+		if (o1 != null && o2 == null) {
+			return false;
+		}
+		if (o1 == null && o2 == null) {
+			return true;
+		}
+		return o1.equals(o2);
+	}
+
+	public static void main(String[] args) {
+		int oneTestDataNum = 100;
+		int value = 10000;
+		int testTimes = 100000;
+		for (int i = 0; i < testTimes; i++) {
+			MyStack<Integer> myStack = new MyStack<>();
+			MyQueue<Integer> myQueue = new MyQueue<>();
+			Stack<Integer> stack = new Stack<>();
+			Queue<Integer> queue = new LinkedList<>();
+			for (int j = 0; j < oneTestDataNum; j++) {
+				int nums = (int) (Math.random() * value);
+				if (stack.isEmpty()) {
+					myStack.push(nums);
+					stack.push(nums);
+				} else {
+					if (Math.random() < 0.5) {
+						myStack.push(nums);
+						stack.push(nums);
+					} else {
+						if (!isEqual(myStack.pop(), stack.pop())) {
+							System.out.println("oops!");
+						}
+					}
+				}
+				int numq = (int) (Math.random() * value);
+				if (stack.isEmpty()) {
+					myQueue.push(numq);
+					queue.offer(numq);
+				} else {
+					if (Math.random() < 0.5) {
+						myQueue.push(numq);
+						queue.offer(numq);
+					} else {
+						if (!isEqual(myQueue.poll(), queue.poll())) {
+							System.out.println("oops!");
+						}
+					}
+				}
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class02/Code04_RingArray.java b/src/class02/Code04_RingArray.java
new file mode 100644
index 0000000..b28c2b7
--- /dev/null
+++ b/src/class02/Code04_RingArray.java
@@ -0,0 +1,50 @@
+package class02;
+
+public class Code04_RingArray {
+
+	public static class MyQueue {
+		private int[] arr;
+		private int pushi;
+		private int polli;
+		private int size;
+		private final int limit;
+
+		public MyQueue(int limit) {
+			arr = new int[limit];
+			pushi = 0;
+			polli = 0;
+			size = 0;
+			this.limit = limit;
+		}
+
+		public void push(int value) {
+			if (size == limit) {
+				throw new RuntimeException("栈满了，不能再加了");
+			}
+			size++;
+			arr[pushi] = value;
+			pushi = nextIndex(pushi);
+		}
+
+		public int pop() {
+			if (size == 0) {
+				throw new RuntimeException("栈空了，不能再拿了");
+			}
+			size--;
+			int ans = arr[polli];
+			polli = nextIndex(polli);
+			return ans;
+		}
+
+		public boolean isEmpty() {
+			return size == 0;
+		}
+
+		// 如果现在的下标是i，返回下一个位置
+		private int nextIndex(int i) {
+			return i < limit - 1 ? i + 1 : 0;
+		}
+
+	}
+
+}
diff --git a/src/class02/Code05_GetMinStack.java b/src/class02/Code05_GetMinStack.java
new file mode 100644
index 0000000..0173d94
--- /dev/null
+++ b/src/class02/Code05_GetMinStack.java
@@ -0,0 +1,105 @@
+package class02;
+
+import java.util.Stack;
+
+public class Code05_GetMinStack {
+
+	public static class MyStack1 {
+		private Stack<Integer> stackData;
+		private Stack<Integer> stackMin;
+
+		public MyStack1() {
+			this.stackData = new Stack<Integer>();
+			this.stackMin = new Stack<Integer>();
+		}
+
+		public void push(int newNum) {
+			if (this.stackMin.isEmpty()) {
+				this.stackMin.push(newNum);
+			} else if (newNum <= this.getmin()) {
+				this.stackMin.push(newNum);
+			}
+			this.stackData.push(newNum);
+		}
+
+		public int pop() {
+			if (this.stackData.isEmpty()) {
+				throw new RuntimeException("Your stack is empty.");
+			}
+			int value = this.stackData.pop();
+			if (value == this.getmin()) {
+				this.stackMin.pop();
+			}
+			return value;
+		}
+
+		public int getmin() {
+			if (this.stackMin.isEmpty()) {
+				throw new RuntimeException("Your stack is empty.");
+			}
+			return this.stackMin.peek();
+		}
+	}
+
+	public static class MyStack2 {
+		private Stack<Integer> stackData;
+		private Stack<Integer> stackMin;
+
+		public MyStack2() {
+			this.stackData = new Stack<Integer>();
+			this.stackMin = new Stack<Integer>();
+		}
+
+		public void push(int newNum) {
+			if (this.stackMin.isEmpty()) {
+				this.stackMin.push(newNum);
+			} else if (newNum < this.getmin()) {
+				this.stackMin.push(newNum);
+			} else {
+				int newMin = this.stackMin.peek();
+				this.stackMin.push(newMin);
+			}
+			this.stackData.push(newNum);
+		}
+
+		public int pop() {
+			if (this.stackData.isEmpty()) {
+				throw new RuntimeException("Your stack is empty.");
+			}
+			this.stackMin.pop();
+			return this.stackData.pop();
+		}
+
+		public int getmin() {
+			if (this.stackMin.isEmpty()) {
+				throw new RuntimeException("Your stack is empty.");
+			}
+			return this.stackMin.peek();
+		}
+	}
+
+	public static void main(String[] args) {
+		MyStack1 stack1 = new MyStack1();
+		stack1.push(3);
+		System.out.println(stack1.getmin());
+		stack1.push(4);
+		System.out.println(stack1.getmin());
+		stack1.push(1);
+		System.out.println(stack1.getmin());
+		System.out.println(stack1.pop());
+		System.out.println(stack1.getmin());
+
+		System.out.println("=============");
+
+		MyStack1 stack2 = new MyStack1();
+		stack2.push(3);
+		System.out.println(stack2.getmin());
+		stack2.push(4);
+		System.out.println(stack2.getmin());
+		stack2.push(1);
+		System.out.println(stack2.getmin());
+		System.out.println(stack2.pop());
+		System.out.println(stack2.getmin());
+	}
+
+}
diff --git a/src/class02/Code06_TwoStacksImplementQueue.java b/src/class02/Code06_TwoStacksImplementQueue.java
new file mode 100644
index 0000000..9144770
--- /dev/null
+++ b/src/class02/Code06_TwoStacksImplementQueue.java
@@ -0,0 +1,60 @@
+package class02;
+
+import java.util.Stack;
+
+public class Code06_TwoStacksImplementQueue {
+
+	public static class TwoStacksQueue {
+		public Stack<Integer> stackPush;
+		public Stack<Integer> stackPop;
+
+		public TwoStacksQueue() {
+			stackPush = new Stack<Integer>();
+			stackPop = new Stack<Integer>();
+		}
+
+		// push栈向pop栈倒入数据
+		private void pushToPop() {
+			if (stackPop.empty()) {
+				while (!stackPush.empty()) {
+					stackPop.push(stackPush.pop());
+				}
+			}
+		}
+
+		public void add(int pushInt) {
+			stackPush.push(pushInt);
+			pushToPop();
+		}
+
+		public int poll() {
+			if (stackPop.empty() && stackPush.empty()) {
+				throw new RuntimeException("Queue is empty!");
+			}
+			pushToPop();
+			return stackPop.pop();
+		}
+
+		public int peek() {
+			if (stackPop.empty() && stackPush.empty()) {
+				throw new RuntimeException("Queue is empty!");
+			}
+			pushToPop();
+			return stackPop.peek();
+		}
+	}
+
+	public static void main(String[] args) {
+		TwoStacksQueue test = new TwoStacksQueue();
+		test.add(1);
+		test.add(2);
+		test.add(3);
+		System.out.println(test.peek());
+		System.out.println(test.poll());
+		System.out.println(test.peek());
+		System.out.println(test.poll());
+		System.out.println(test.peek());
+		System.out.println(test.poll());
+	}
+
+}
diff --git a/src/class02/Code07_TwoQueueImplementStack.java b/src/class02/Code07_TwoQueueImplementStack.java
new file mode 100644
index 0000000..49a87c1
--- /dev/null
+++ b/src/class02/Code07_TwoQueueImplementStack.java
@@ -0,0 +1,90 @@
+package class02;
+
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.Stack;
+
+public class Code07_TwoQueueImplementStack {
+
+	public static class TwoQueueStack<T> {
+		public Queue<T> queue;
+		public Queue<T> help;
+
+		public TwoQueueStack() {
+			queue = new LinkedList<>();
+			help = new LinkedList<>();
+		}
+
+		public void push(T value) {
+			queue.offer(value);
+		}
+
+		public T poll() {
+			while (queue.size() > 1) {
+				help.offer(queue.poll());
+			}
+			T ans = queue.poll();
+			Queue<T> tmp = queue;
+			queue = help;
+			help = tmp;
+			return ans;
+		}
+
+		public T peek() {
+			while (queue.size() > 1) {
+				help.offer(queue.poll());
+			}
+			T ans = queue.poll();
+			help.offer(ans);
+			Queue<T> tmp = queue;
+			queue = help;
+			help = tmp;
+			return ans;
+		}
+
+		public boolean isEmpty() {
+			return queue.isEmpty();
+		}
+
+	}
+
+	public static void main(String[] args) {
+		System.out.println("test begin");
+		TwoQueueStack<Integer> myStack = new TwoQueueStack<>();
+		Stack<Integer> test = new Stack<>();
+		int testTime = 1000000;
+		int max = 1000000;
+		for (int i = 0; i < testTime; i++) {
+			if (myStack.isEmpty()) {
+				if (!test.isEmpty()) {
+					System.out.println("Oops");
+				}
+				int num = (int) (Math.random() * max);
+				myStack.push(num);
+				test.push(num);
+			} else {
+				if (Math.random() < 0.25) {
+					int num = (int) (Math.random() * max);
+					myStack.push(num);
+					test.push(num);
+				} else if (Math.random() < 0.5) {
+					if (!myStack.peek().equals(test.peek())) {
+						System.out.println("Oops");
+					}
+				} else if (Math.random() < 0.75) {
+					if (!myStack.poll().equals(test.pop())) {
+						System.out.println("Oops");
+					}
+				} else {
+					if (myStack.isEmpty() != test.isEmpty()) {
+						System.out.println("Oops");
+					}
+				}
+			}
+		}
+
+		System.out.println("test finish!");
+
+	}
+
+}
diff --git a/src/class02/Code08_GetMax.java b/src/class02/Code08_GetMax.java
new file mode 100644
index 0000000..cd7141f
--- /dev/null
+++ b/src/class02/Code08_GetMax.java
@@ -0,0 +1,21 @@
+package class02;
+
+public class Code08_GetMax {
+
+	// 求arr中的最大值
+	public static int getMax(int[] arr) {
+		return process(arr, 0, arr.length - 1);
+	}
+
+	// arr[L..R]范围上求最大值  L ... R   N
+	public static int process(int[] arr, int L, int R) {
+		if (L == R) { // arr[L..R]范围上只有一个数，直接返回，base case
+			return arr[L];
+		}
+		int mid = L + ((R - L) >> 1); // 中点   	1
+		int leftMax = process(arr, L, mid);
+		int rightMax = process(arr, mid + 1, R);
+		return Math.max(leftMax, rightMax);
+	}
+
+}
diff --git a/src/class02/HashMapAndSortedMap.java b/src/class02/HashMapAndSortedMap.java
new file mode 100644
index 0000000..717b81b
--- /dev/null
+++ b/src/class02/HashMapAndSortedMap.java
@@ -0,0 +1,112 @@
+package class02;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.TreeMap;
+
+public class HashMapAndSortedMap {
+	
+	
+	public static class Node{
+		public int value;
+		public Node(int v) {
+			 value = v;
+		}
+	}
+	
+	public static void main(String[] args) {
+		// UnSortedMap
+		HashMap<Integer, String> map = new HashMap<>();
+		map.put(1000000, "我是1000000");
+		map.put(2, "我是2");
+		map.put(3, "我是3");
+		map.put(4, "我是4");
+		map.put(5, "我是5");
+		map.put(6, "我是6");
+		map.put(1000000, "我是1000001");
+		
+		System.out.println(map.containsKey(1));
+		System.out.println(map.containsKey(10));
+		
+		System.out.println(map.get(4));
+		System.out.println(map.get(10));
+		
+		map.put(4, "他是4");
+		System.out.println(map.get(4));
+		
+		map.remove(4);
+		System.out.println(map.get(4));
+		
+		
+		
+		//       key
+		HashSet<String>  set = new HashSet<>();
+		set.add("abc");
+		set.contains("abc");
+		set.remove("abc");
+		
+		// 哈希表，增、删、改、查，在使用时，O（1）
+		
+		
+		System.out.println("=====================");
+		
+		
+		int a = 100000;
+		int b = 100000;
+		System.out.println(a == b);
+		
+		Integer c = 100000;
+		Integer d = 100000;
+		System.out.println(c.equals(d));
+		
+		Integer e = 127;  //  - 128  ~  127
+		Integer f = 127;
+		System.out.println(e == f);
+		
+		
+		
+		HashMap<Node, String> map2 = new HashMap<>();
+		Node node1 = new Node(1);
+		Node node2 = node1;
+		map2.put(node1, "我是node1");
+		map2.put(node2, "我是node1");
+		System.out.println(map2.size());
+		
+		System.out.println("======================");
+		
+		TreeMap<Integer, String> treeMap = new TreeMap<>();
+		
+		treeMap.put(3, "我是3");
+		treeMap.put(4, "我是4");
+		treeMap.put(8, "我是8");
+		treeMap.put(5, "我是5");
+		treeMap.put(7, "我是7");
+		treeMap.put(1, "我是1");
+		treeMap.put(2, "我是2");
+
+		System.out.println(treeMap.containsKey(1));
+		System.out.println(treeMap.containsKey(10));
+		
+		System.out.println(treeMap.get(4));
+		System.out.println(treeMap.get(10));
+		
+		treeMap.put(4, "他是4");
+		System.out.println(treeMap.get(4));
+		
+		treeMap.remove(4);
+		System.out.println(treeMap.get(4));
+		
+		System.out.println(treeMap.firstKey());
+		System.out.println(treeMap.lastKey());
+		// <= 4
+		System.out.println(treeMap.floorKey(4));
+		// >= 4
+		System.out.println(treeMap.ceilingKey(4));
+		
+		// O(logN)	
+		
+	}
+	
+	
+	
+}
diff --git a/src/class03/Code01_MergeSort.java b/src/class03/Code01_MergeSort.java
new file mode 100644
index 0000000..50c1664
--- /dev/null
+++ b/src/class03/Code01_MergeSort.java
@@ -0,0 +1,147 @@
+package class03;
+
+public class Code01_MergeSort {
+
+
+
+	// 递归方法实现
+	public static void mergeSort1(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return;
+		}
+		process(arr, 0, arr.length - 1);
+	}
+
+	// arr[L...R]范围上，变成有序的
+	// L...R    N    T(N) = 2*T(N/2) + O(N)  ->
+	public static void process(int[] arr, int L, int R) {
+		if (L == R) { // base case
+			return;
+		}
+		int mid = L + ((R - L) >> 1);
+		process(arr, L, mid);
+		process(arr, mid + 1, R);
+		merge(arr, L, mid, R);
+	}
+
+	public static void merge(int[] arr, int L, int M, int R) {
+		int[] help = new int[R - L + 1];
+		int i = 0;
+		int p1 = L;
+		int p2 = M + 1;
+		while (p1 <= M && p2 <= R) {
+			help[i++] = arr[p1] <= arr[p2] ? arr[p1++] : arr[p2++];
+		}
+		// 要么p1越界了，要么p2越界了
+		while (p1 <= M) {
+			help[i++] = arr[p1++];
+		}
+		while (p2 <= R) {
+			help[i++] = arr[p2++];
+		}
+		for (i = 0; i < help.length; i++) {
+			arr[L + i] = help[i];
+		}
+	}
+
+	// 非递归方法实现
+	public static void mergeSort2(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return;
+		}
+		int N = arr.length;
+		int mergeSize = 1;// 当前有序的，左组长度
+		while (mergeSize < N) { // log N
+			int L = 0;
+			// 0.... 
+			while (L < N) {
+				// L...M  左组（mergeSize）
+				int M = L + mergeSize - 1;
+				if (M >= N) {
+					break;
+				}
+				//  L...M   M+1...R(mergeSize)
+				int R = Math.min(M + mergeSize, N - 1);
+				merge(arr, L, M, R);
+				L = R + 1;
+			}
+			if (mergeSize > N / 2) {
+				break;
+			}
+			mergeSize <<= 1;
+		}
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[] copyArray(int[] arr) {
+		if (arr == null) {
+			return null;
+		}
+		int[] res = new int[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			res[i] = arr[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static boolean isEqual(int[] arr1, int[] arr2) {
+		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
+			return false;
+		}
+		if (arr1 == null && arr2 == null) {
+			return true;
+		}
+		if (arr1.length != arr2.length) {
+			return false;
+		}
+		for (int i = 0; i < arr1.length; i++) {
+			if (arr1[i] != arr2[i]) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	// for test
+	public static void main(String[] args) {
+		int testTime = 500000;
+		int maxSize = 100;
+		int maxValue = 100;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr1 = generateRandomArray(maxSize, maxValue);
+			int[] arr2 = copyArray(arr1);
+			mergeSort1(arr1);
+			mergeSort2(arr2);
+			if (!isEqual(arr1, arr2)) {
+				succeed = false;
+				printArray(arr1);
+				printArray(arr2);
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Oops!");
+	}
+
+}
diff --git a/src/class03/Code02_SmallSum.java b/src/class03/Code02_SmallSum.java
new file mode 100644
index 0000000..bddae7d
--- /dev/null
+++ b/src/class03/Code02_SmallSum.java
@@ -0,0 +1,137 @@
+package class03;
+
+public class Code02_SmallSum {
+
+	public static int smallSum(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return 0;
+		}
+		return process(arr, 0, arr.length - 1);
+	}
+
+	// arr[L..R]既要排好序，也要求小和返回
+	// 所有merge时，产生的小和，累加
+	// 左 排序   merge
+	// 右 排序  merge
+	// merge
+	public static int process(int[] arr, int l, int r) {
+		if (l == r) {
+			return 0;
+		}
+		// l < r
+		int mid = l + ((r - l) >> 1);
+		return 
+				process(arr, l, mid) 
+				+ 
+				process(arr, mid + 1, r) 
+				+ 
+				merge(arr, l, mid, r);
+	}
+
+	public static int merge(int[] arr, int L, int m, int r) {
+		int[] help = new int[r - L + 1];
+		int i = 0;
+		int p1 = L;
+		int p2 = m + 1;
+		int res = 0;
+		while (p1 <= m && p2 <= r) {
+			res += arr[p1] < arr[p2] ? (r - p2 + 1) * arr[p1] : 0;
+			help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
+		}
+		while (p1 <= m) {
+			help[i++] = arr[p1++];
+		}
+		while (p2 <= r) {
+			help[i++] = arr[p2++];
+		}
+		for (i = 0; i < help.length; i++) {
+			arr[L + i] = help[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static int comparator(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return 0;
+		}
+		int res = 0;
+		for (int i = 1; i < arr.length; i++) {
+			for (int j = 0; j < i; j++) {
+				res += arr[j] < arr[i] ? arr[j] : 0;
+			}
+		}
+		return res;
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[] copyArray(int[] arr) {
+		if (arr == null) {
+			return null;
+		}
+		int[] res = new int[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			res[i] = arr[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static boolean isEqual(int[] arr1, int[] arr2) {
+		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
+			return false;
+		}
+		if (arr1 == null && arr2 == null) {
+			return true;
+		}
+		if (arr1.length != arr2.length) {
+			return false;
+		}
+		for (int i = 0; i < arr1.length; i++) {
+			if (arr1[i] != arr2[i]) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	// for test
+	public static void main(String[] args) {
+		int testTime = 500000;
+		int maxSize = 100;
+		int maxValue = 100;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr1 = generateRandomArray(maxSize, maxValue);
+			int[] arr2 = copyArray(arr1);
+			if (smallSum(arr1) != comparator(arr2)) {
+				succeed = false;
+				printArray(arr1);
+				printArray(arr2);
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Fucking fucked!");
+	}
+
+}
diff --git a/src/class03/Code03_PartitionAndQuickSort.java b/src/class03/Code03_PartitionAndQuickSort.java
new file mode 100644
index 0000000..ae8fa78
--- /dev/null
+++ b/src/class03/Code03_PartitionAndQuickSort.java
@@ -0,0 +1,178 @@
+package class03;
+
+public class Code03_PartitionAndQuickSort {
+
+	public static void swap(int[] arr, int i, int j) {
+		int tmp = arr[i];
+		arr[i] = arr[j];
+		arr[j] = tmp;
+	}
+
+	public static int partition(int[] arr, int L, int R) {
+		if (L > R) {
+			return -1;
+		}
+		if (L == R) {
+			return L;
+		}
+		int lessEqual = L - 1;
+		int index = L;
+		while (index < R) {
+			if (arr[index] <= arr[R]) {
+				swap(arr, index, ++lessEqual);
+			}
+			index++;
+		}
+		swap(arr, ++lessEqual, R);
+		return lessEqual;
+	}
+
+	// arr[L...R] 玩荷兰国旗问题的划分，以arr[R]做划分值
+	//  <arr[R]  ==arr[R]  > arr[R]
+	public static int[] netherlandsFlag(int[] arr, int L, int R) {
+		if (L > R) {
+			return new int[] { -1, -1 };
+		}
+		if (L == R) {
+			return new int[] { L, R };
+		}
+		int less = L - 1; // < 区 右边界
+		int more = R;     // > 区 左边界
+		int index = L;
+		while (index < more) {
+			if (arr[index] == arr[R]) {
+				index++;
+			} else if (arr[index] < arr[R]) {
+				swap(arr, index++, ++less);
+			} else { // >
+				swap(arr, index, --more);
+			}
+		}
+		swap(arr, more, R);
+		return new int[] { less + 1, more };
+	}
+
+	public static void quickSort1(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return;
+		}
+		process1(arr, 0, arr.length - 1);
+	}
+
+	public static void process1(int[] arr, int L, int R) {
+		if (L >= R) {
+			return;
+		}
+		// L..R partition arr[R]  [   <=arr[R]   arr[R]    >arr[R]  ]
+		int M = partition(arr, L, R);
+		process1(arr, L, M - 1);
+		process1(arr, M + 1, R);
+	}
+
+	public static void quickSort2(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return;
+		}
+		process2(arr, 0, arr.length - 1);
+	}
+
+	public static void process2(int[] arr, int L, int R) {
+		if (L >= R) {
+			return;
+		}
+		int[] equalArea = netherlandsFlag(arr, L, R);
+		process2(arr, L, equalArea[0] - 1);
+		process2(arr, equalArea[1] + 1, R);
+	}
+
+	public static void quickSort3(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return;
+		}
+		process3(arr, 0, arr.length - 1);
+	}
+
+	public static void process3(int[] arr, int L, int R) {
+		if (L >= R) {
+			return;
+		}
+		swap(arr, L + (int) (Math.random() * (R - L + 1)), R);
+		int[] equalArea = netherlandsFlag(arr, L, R);
+		process3(arr, L, equalArea[0] - 1);
+		process3(arr, equalArea[1] + 1, R);
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[] copyArray(int[] arr) {
+		if (arr == null) {
+			return null;
+		}
+		int[] res = new int[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			res[i] = arr[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static boolean isEqual(int[] arr1, int[] arr2) {
+		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
+			return false;
+		}
+		if (arr1 == null && arr2 == null) {
+			return true;
+		}
+		if (arr1.length != arr2.length) {
+			return false;
+		}
+		for (int i = 0; i < arr1.length; i++) {
+			if (arr1[i] != arr2[i]) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	// for test
+	public static void main(String[] args) {
+		int testTime = 500000;
+		int maxSize = 100;
+		int maxValue = 100;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr1 = generateRandomArray(maxSize, maxValue);
+			int[] arr2 = copyArray(arr1);
+			int[] arr3 = copyArray(arr1);
+			quickSort1(arr1);
+			quickSort2(arr2);
+			quickSort3(arr3);
+			if (!isEqual(arr1, arr2) || !isEqual(arr2, arr3)) {
+				succeed = false;
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Oops!");
+
+	}
+
+}
diff --git a/src/class04/Code01_Comparator.java b/src/class04/Code01_Comparator.java
new file mode 100644
index 0000000..09c7035
--- /dev/null
+++ b/src/class04/Code01_Comparator.java
@@ -0,0 +1,213 @@
+package class04;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.PriorityQueue;
+import java.util.TreeSet;
+
+public class Code01_Comparator {
+
+	public static class Student {
+		public String name;
+		public int id;
+		public int age;
+
+		public Student(String name, int id, int age) {
+			this.name = name;
+			this.id = id;
+			this.age = age;
+		}
+	}
+
+	public static class IdAscendingComparator 
+	
+	implements Comparator<Student> {
+
+		// 返回负数的时候，第一个参数排在前面
+		// 返回正数的时候，第二个参数排在前面
+		// 返回0的时候，谁在前面无所谓
+		@Override
+		public int compare(Student o1, Student o2) {
+			return o1.id - o2.id;
+		}
+
+	}
+
+	public static class IdDescendingComparator implements Comparator<Student> {
+
+		@Override
+		public int compare(Student o1, Student o2) {
+			return o2.id - o1.id;
+		}
+
+	}
+
+	public static class AgeAscendingComparator implements Comparator<Student> {
+
+		@Override
+		public int compare(Student o1, Student o2) {
+			return o1.age - o2.age;
+		}
+
+	}
+
+	public static class AgeDescendingComparator implements Comparator<Student> {
+
+		@Override
+		public int compare(Student o1, Student o2) {
+			return o2.age - o1.age;
+		}
+
+	}
+	
+	
+	public static class AgeShengIdSheng implements Comparator<Student> {
+
+		@Override
+		public int compare(Student o1, Student o2) {
+			return o1.age != o2.age ? (o1.age - o2.age) 
+					: (o1.id - o2.id);
+		}
+
+	}
+	
+	
+	// 先按照id排序，id小的，放前面；
+	// id一样，age大的，前面；
+	public static class IdInAgeDe implements Comparator<Student> {
+
+		@Override
+		public int compare(Student o1, Student o2) {
+			return o1.id != o2.id ? o1.id - o2.id  : (  o2.age - o1.age  );
+		}
+
+	}
+	
+
+	public static void printStudents(Student[] students) {
+		for (Student student : students) {
+			System.out.println("Name : " + student.name + ", Id : " + student.id + ", Age : " + student.age);
+		}
+	}
+
+	public static void printArray(Integer[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	public static class MyComp implements Comparator<Integer> {
+
+		@Override
+		public int compare(Integer o1, Integer o2) {
+			return o2 - o1;
+		}
+
+	}
+	
+	
+	public static class AComp implements Comparator<Integer>{
+
+		// 如果返回负数，认为第一个参数应该拍在前面
+		// 如果返回正数，认为第二个参数应该拍在前面
+		// 如果返回0，认为谁放前面都行
+		@Override
+		public int compare(Integer arg0, Integer arg1) {
+			
+			return arg1 - arg0;
+			
+//			return 0;
+		}
+		
+	}
+	
+
+	public static void main(String[] args) {
+		
+		Integer[] arr = {5,4,3,2,7,9,1,0};
+		
+		Arrays.sort(arr, new AComp());
+		
+		for(int i = 0 ;i < arr.length;i++) {
+			System.out.println(arr[i]);
+		}
+		
+		System.out.println("===========================");
+		
+		Student student1 = new Student("A", 2, 20);
+		Student student2 = new Student("B", 3, 21);
+		Student student3 = new Student("C", 1, 22);
+
+		Student[] students = new Student[] { student1, student2, student3 };
+		System.out.println("第一条打印");
+		
+		
+		Arrays.sort(students, new IdAscendingComparator());
+		
+		
+		printStudents(students);
+		System.out.println("===========================");
+		
+		
+
+		Arrays.sort(students, new IdDescendingComparator());
+		printStudents(students);
+		System.out.println("===========================");
+
+		Arrays.sort(students, new AgeAscendingComparator());
+		printStudents(students);
+		System.out.println("===========================");
+////
+////		Arrays.sort(students, new AgeDescendingComparator());
+////		printStudents(students);
+////		System.out.println("===========================");
+//		
+//		Arrays.sort(students, new AgeShengIdSheng());
+//		printStudents(students);
+//		
+//		System.out.println("===========================");
+//		System.out.println("===========================");
+//		System.out.println("===========================");
+//
+//		PriorityQueue<Student> maxHeapBasedAge = new PriorityQueue<>(new AgeDescendingComparator());
+//		maxHeapBasedAge.add(student1);
+//		maxHeapBasedAge.add(student2);
+//		maxHeapBasedAge.add(student3);
+//		while (!maxHeapBasedAge.isEmpty()) {
+//			Student student = maxHeapBasedAge.poll();
+//			System.out.println("Name : " + student.name + ", Id : " + student.id + ", Age : " + student.age);
+//		}
+//		System.out.println("===========================");
+
+		PriorityQueue<Student> minHeapBasedId
+		= new PriorityQueue<>(new AgeAscendingComparator());
+		minHeapBasedId.add(student1);
+		minHeapBasedId.add(student2);
+		minHeapBasedId.add(student3);
+		while (!minHeapBasedId.isEmpty()) {
+			Student student = minHeapBasedId.poll();
+			System.out.println("Name : " + student.name + ", Id : " + student.id + ", Age : " + student.age);
+		}
+		System.out.println("===========================");
+		System.out.println("===========================");
+		System.out.println("===========================");
+
+		TreeSet<Student> treeAgeDescending = new TreeSet<>(new AgeAscendingComparator());
+		treeAgeDescending.add(student1);
+		treeAgeDescending.add(student2);
+		treeAgeDescending.add(student3);
+
+		Student studentFirst = treeAgeDescending.first();
+		System.out.println("Name : " + studentFirst.name + ", Id : " + studentFirst.id + ", Age : " + studentFirst.age);
+
+		Student studentLast = treeAgeDescending.last();
+		System.out.println("Name : " + studentLast.name + ", Id : " + studentLast.id + ", Age : " + studentLast.age);
+		System.out.println("===========================");
+
+	}
+
+}
diff --git a/src/class04/Code02_Heap01.java b/src/class04/Code02_Heap01.java
new file mode 100644
index 0000000..715289e
--- /dev/null
+++ b/src/class04/Code02_Heap01.java
@@ -0,0 +1,160 @@
+package class04;
+
+public class Code02_Heap01 {
+
+	public static class MyMaxHeap {
+		private int[] heap;
+		private final int limit;
+		private int heapSize;
+
+		public MyMaxHeap(int limit) {
+			heap = new int[limit];
+			this.limit = limit;
+			heapSize = 0;
+		}
+
+		public boolean isEmpty() {
+			return heapSize == 0;
+		}
+
+		public boolean isFull() {
+			return heapSize == limit;
+		}
+
+		public void push(int value) {
+			if (heapSize == limit) {
+				throw new RuntimeException("heap is full");
+			}
+			heap[heapSize] = value;
+			// value  heapSize
+			heapInsert(heap, heapSize++);
+		}
+
+		// 用户此时，让你返回最大值，并且在大根堆中，把最大值删掉
+		// 剩下的数，依然保持大根堆组织
+		public int pop() {
+			int ans = heap[0];
+			swap(heap, 0, --heapSize);
+			heapify(heap, 0, heapSize);
+			return ans;
+		}
+
+		private void heapInsert(int[] arr, int index) {
+			// arr[index]
+			// arr[index] 不比 arr[index父]大了 ， 停
+			// index = 0;
+			while (arr[index] > arr[(index - 1) / 2]) {
+				swap(arr, index, (index - 1) / 2);
+				index = (index - 1) / 2;
+			}
+		}
+
+		// 从index位置，往下看，不断的下沉，
+		// 停：我的孩子都不再比我大；已经没孩子了
+		private void heapify(int[] arr, int index, int heapSize) {
+			int left = index * 2 + 1;
+			while (left < heapSize) {
+				// 左右两个孩子中，谁大，谁把自己的下标给largest
+				// 右  ->  1) 有右孩子   && 2）右孩子的值比左孩子大才行
+				// 否则，左
+				int largest = left + 1 < heapSize && arr[left + 1] > arr[left] ? left + 1 : left;
+				largest = arr[largest] > arr[index] ? largest : index;
+				if (largest == index) {
+					break;
+				}
+				swap(arr, largest, index);
+				index = largest;
+				left = index * 2 + 1;
+			}
+		}
+
+		private void swap(int[] arr, int i, int j) {
+			int tmp = arr[i];
+			arr[i] = arr[j];
+			arr[j] = tmp;
+		}
+
+	}
+
+	public static class RightMaxHeap {
+		private int[] arr;
+		private final int limit;
+		private int size;
+
+		public RightMaxHeap(int limit) {
+			arr = new int[limit];
+			this.limit = limit;
+			size = 0;
+		}
+
+		public boolean isEmpty() {
+			return size == 0;
+		}
+
+		public boolean isFull() {
+			return size == limit;
+		}
+
+		public void push(int value) {
+			if (size == limit) {
+				throw new RuntimeException("heap is full");
+			}
+			arr[size++] = value;
+		}
+
+		public int pop() {
+			int maxIndex = 0;
+			for (int i = 1; i < size; i++) {
+				if (arr[i] > arr[maxIndex]) {
+					maxIndex = i;
+				}
+			}
+			int ans = arr[maxIndex];
+			arr[maxIndex] = arr[--size];
+			return ans;
+		}
+
+	}
+
+	public static void main(String[] args) {
+		int value = 1000;
+		int limit = 100;
+		int testTimes = 1000000;
+		for (int i = 0; i < testTimes; i++) {
+			int curLimit = (int) (Math.random() * limit) + 1;
+			MyMaxHeap my = new MyMaxHeap(curLimit);
+			RightMaxHeap test = new RightMaxHeap(curLimit);
+			int curOpTimes = (int) (Math.random() * limit);
+			for (int j = 0; j < curOpTimes; j++) {
+				if (my.isEmpty() != test.isEmpty()) {
+					System.out.println("Oops!");
+				}
+				if (my.isFull() != test.isFull()) {
+					System.out.println("Oops!");
+				}
+				if (my.isEmpty()) {
+					int curValue = (int) (Math.random() * value);
+					my.push(curValue);
+					test.push(curValue);
+				} else if (my.isFull()) {
+					if (my.pop() != test.pop()) {
+						System.out.println("Oops!");
+					}
+				} else {
+					if (Math.random() < 0.5) {
+						int curValue = (int) (Math.random() * value);
+						my.push(curValue);
+						test.push(curValue);
+					} else {
+						if (my.pop() != test.pop()) {
+							System.out.println("Oops!");
+						}
+					}
+				}
+			}
+		}
+		System.out.println("finish!");
+
+	}
+
+}
diff --git a/src/class04/Code03_Heap02.java b/src/class04/Code03_Heap02.java
new file mode 100644
index 0000000..aa0fba5
--- /dev/null
+++ b/src/class04/Code03_Heap02.java
@@ -0,0 +1,256 @@
+package class04;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.PriorityQueue;
+
+public class Code03_Heap02 {
+
+	// 堆
+	public static class MyHeap<T> {
+		private ArrayList<T> heap;
+		private HashMap<T, Integer> indexMap;
+		private int heapSize;
+		private Comparator<? super T> comparator;
+
+		public MyHeap(Comparator<? super T> com) {
+			heap = new ArrayList<>();
+			indexMap = new HashMap<>();
+			heapSize = 0;
+			comparator = com;
+		}
+
+		public boolean isEmpty() {
+			return heapSize == 0;
+		}
+
+		public int size() {
+			return heapSize;
+		}
+
+		public boolean contains(T key) {
+			return indexMap.containsKey(key);
+		}
+
+		public void push(T value) {
+			heap.add(value);
+			indexMap.put(value, heapSize);
+			heapInsert(heapSize++);
+		}
+
+		public T pop() {
+			T ans = heap.get(0);
+			int end = heapSize - 1;
+			swap(0, end);
+			heap.remove(end);
+			indexMap.remove(ans);
+			heapify(0, --heapSize);
+			return ans;
+		}
+
+		public void resign(T value) {
+			int valueIndex = indexMap.get(value);
+			heapInsert(valueIndex);
+			heapify(valueIndex, heapSize);
+		}
+
+		private void heapInsert(int index) {
+			while (comparator.compare(heap.get(index), heap.get((index - 1) / 2)) < 0) {
+				swap(index, (index - 1) / 2);
+				index = (index - 1) / 2;
+			}
+		}
+
+		private void heapify(int index, int heapSize) {
+			int left = index * 2 + 1;
+			while (left < heapSize) {
+				int largest = left + 1 < heapSize && (comparator.compare(heap.get(left + 1), heap.get(left)) < 0)
+						? left + 1
+						: left;
+				largest = comparator.compare(heap.get(largest), heap.get(index)) < 0 ? largest : index;
+				if (largest == index) {
+					break;
+				}
+				swap(largest, index);
+				index = largest;
+				left = index * 2 + 1;
+			}
+		}
+
+		private void swap(int i, int j) {
+			T o1 = heap.get(i);
+			T o2 = heap.get(j);
+			heap.set(i, o2);
+			heap.set(j, o1);
+			indexMap.put(o1, j);
+			indexMap.put(o2, i);
+		}
+
+	}
+
+	public static class Student {
+		public int classNo;
+		public int age;
+		public int id;
+
+		public Student(int c, int a, int i) {
+			classNo = c;
+			age = a;
+			id = i;
+		}
+
+	}
+
+	public static class StudentComparator implements Comparator<Student> {
+
+		@Override
+		public int compare(Student o1, Student o2) {
+			return o1.age - o2.age;
+		}
+
+	}
+
+	public static void main(String[] args) {
+		Student s1 = null;
+		Student s2 = null;
+		Student s3 = null;
+		Student s4 = null;
+		Student s5 = null;
+		Student s6 = null;
+
+		s1 = new Student(2, 50, 11111);
+		s2 = new Student(1, 60, 22222);
+		s3 = new Student(6, 10, 33333);
+		s4 = new Student(3, 20, 44444);
+		s5 = new Student(7, 72, 55555);
+		s6 = new Student(1, 14, 66666);
+
+		PriorityQueue<Student> heap = new PriorityQueue<>(new StudentComparator());
+		heap.add(s1);
+		heap.add(s2);
+		heap.add(s3);
+		heap.add(s4);
+		heap.add(s5);
+		heap.add(s6);
+		while (!heap.isEmpty()) {
+			Student cur = heap.poll();
+			System.out.println(cur.classNo + "," + cur.age + "," + cur.id);
+		}
+
+		System.out.println("===============");
+
+		MyHeap<Student> myHeap = new MyHeap<>(new StudentComparator());
+		myHeap.push(s1);
+		myHeap.push(s2);
+		myHeap.push(s3);
+		myHeap.push(s4);
+		myHeap.push(s5);
+		myHeap.push(s6);
+		while (!myHeap.isEmpty()) {
+			Student cur = myHeap.pop();
+			System.out.println(cur.classNo + "," + cur.age + "," + cur.id);
+		}
+
+		System.out.println("===============");
+
+		s1 = new Student(2, 50, 11111);
+		s2 = new Student(1, 60, 22222);
+		s3 = new Student(6, 10, 33333);
+		s4 = new Student(3, 20, 44444);
+		s5 = new Student(7, 72, 55555);
+		s6 = new Student(1, 14, 66666);
+
+		heap = new PriorityQueue<>(new StudentComparator());
+
+		heap.add(s1);
+		heap.add(s2);
+		heap.add(s3);
+		heap.add(s4);
+		heap.add(s5);
+		heap.add(s6);
+
+		s2.age = 6;
+		s4.age = 12;
+		s5.age = 10;
+		s6.age = 84;
+
+		while (!heap.isEmpty()) {
+			Student cur = heap.poll();
+			System.out.println(cur.classNo + "," + cur.age + "," + cur.id);
+		}
+
+		System.out.println("===============");
+
+		s1 = new Student(2, 50, 11111);
+		s2 = new Student(1, 60, 22222);
+		s3 = new Student(6, 10, 33333);
+		s4 = new Student(3, 20, 44444);
+		s5 = new Student(7, 72, 55555);
+		s6 = new Student(1, 14, 66666);
+
+		myHeap = new MyHeap<>(new StudentComparator());
+
+		myHeap.push(s1);
+		myHeap.push(s2);
+		myHeap.push(s3);
+		myHeap.push(s4);
+		myHeap.push(s5);
+		myHeap.push(s6);
+
+		s2.age = 6;
+		myHeap.resign(s2);
+		s4.age = 12;
+		myHeap.resign(s4);
+		s5.age = 10;
+		myHeap.resign(s5);
+		s6.age = 84;
+		myHeap.resign(s6);
+
+		while (!myHeap.isEmpty()) {
+			Student cur = myHeap.pop();
+			System.out.println(cur.classNo + "," + cur.age + "," + cur.id);
+		}
+		
+		
+		
+		// 对数器
+		System.out.println("test begin");
+		int maxValue = 100000;
+		int pushTime = 1000000;
+		int resignTime = 100;
+		MyHeap<Student> test = new MyHeap<>(new StudentComparator());
+		ArrayList<Student> list = new ArrayList<>();
+		for(int i = 0 ; i < pushTime; i++) {
+			Student cur = new Student(1,(int) (Math.random() * maxValue), 1000);
+			list.add(cur);
+			test.push(cur);
+		}
+		for(int i = 0 ; i < resignTime; i++) {
+			int index = (int)(Math.random() * pushTime);
+			list.get(index).age = (int) (Math.random() * maxValue);
+			test.resign(list.get(index));
+		}
+		int preAge = Integer.MIN_VALUE;
+		while(test.isEmpty()) {
+			Student cur = test.pop();
+			if(cur.age < preAge) {
+				System.out.println("Oops!");
+			}
+			preAge = cur.age;
+		}
+		System.out.println("test finish");
+		
+		
+		
+		
+		
+		
+		
+		
+		
+		
+
+	}
+
+}
diff --git a/src/class04/Code04_HeapSort.java b/src/class04/Code04_HeapSort.java
new file mode 100644
index 0000000..1b65638
--- /dev/null
+++ b/src/class04/Code04_HeapSort.java
@@ -0,0 +1,157 @@
+package class04;
+
+import java.util.Arrays;
+import java.util.PriorityQueue;
+
+public class Code04_HeapSort {
+
+	// 堆排序额外空间复杂度O(1)
+	public static void heapSort(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return;
+		}
+		// O(N*logN)
+//		for (int i = 0; i < arr.length; i++) { // O(N)
+//			heapInsert(arr, i); // O(logN)
+//		}
+		for (int i = arr.length - 1; i >= 0; i--) {
+			heapify(arr, i, arr.length);
+		}
+		int heapSize = arr.length;
+		swap(arr, 0, --heapSize);
+		// O(N*logN)
+		while (heapSize > 0) { // O(N)
+			heapify(arr, 0, heapSize); // O(logN)
+			swap(arr, 0, --heapSize); // O(1)
+		}
+	}
+
+	// arr[index]刚来的数，往上
+	public static void heapInsert(int[] arr, int index) {
+		while (arr[index] > arr[(index - 1) / 2]) {
+			swap(arr, index, (index - 1) / 2);
+			index = (index - 1) / 2;
+		}
+	}
+
+	// arr[index]位置的数，能否往下移动
+	public static void heapify(int[] arr, int index, int heapSize) {
+		int left = index * 2 + 1; // 左孩子的下标
+		while (left < heapSize) { // 下方还有孩子的时候
+			// 两个孩子中，谁的值大，把下标给largest
+			// 1）只有左孩子，left -> largest
+			// 2) 同时有左孩子和右孩子，右孩子的值<= 左孩子的值，left -> largest
+			// 3) 同时有左孩子和右孩子并且右孩子的值> 左孩子的值， right -> largest
+			int largest = left + 1 < heapSize && arr[left + 1] > arr[left] ? left + 1 : left;
+			// 父和较大的孩子之间，谁的值大，把下标给largest
+			largest = arr[largest] > arr[index] ? largest : index;
+			if (largest == index) {
+				break;
+			}
+			swap(arr, largest, index);
+			index = largest;
+			left = index * 2 + 1;
+		}
+	}
+
+	public static void swap(int[] arr, int i, int j) {
+		int tmp = arr[i];
+		arr[i] = arr[j];
+		arr[j] = tmp;
+	}
+
+	// for test
+	public static void comparator(int[] arr) {
+		Arrays.sort(arr);
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[] copyArray(int[] arr) {
+		if (arr == null) {
+			return null;
+		}
+		int[] res = new int[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			res[i] = arr[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static boolean isEqual(int[] arr1, int[] arr2) {
+		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
+			return false;
+		}
+		if (arr1 == null && arr2 == null) {
+			return true;
+		}
+		if (arr1.length != arr2.length) {
+			return false;
+		}
+		for (int i = 0; i < arr1.length; i++) {
+			if (arr1[i] != arr2[i]) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	// for test
+	public static void main(String[] args) {
+
+		// 默认小根堆
+		PriorityQueue<Integer> heap = new PriorityQueue<>();
+		heap.add(6);
+		heap.add(8);
+		heap.add(0);
+		heap.add(2);
+		heap.add(9);
+		heap.add(1);
+
+		while (!heap.isEmpty()) {
+			System.out.println(heap.poll());
+		}
+
+		int testTime = 500000;
+		int maxSize = 100;
+		int maxValue = 100;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr1 = generateRandomArray(maxSize, maxValue);
+			int[] arr2 = copyArray(arr1);
+			heapSort(arr1);
+			comparator(arr2);
+			if (!isEqual(arr1, arr2)) {
+				succeed = false;
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Fucking fucked!");
+
+		int[] arr = generateRandomArray(maxSize, maxValue);
+		printArray(arr);
+		heapSort(arr);
+		printArray(arr);
+	}
+
+}
diff --git a/src/class04/Code05_SortArrayDistanceLessK.java b/src/class04/Code05_SortArrayDistanceLessK.java
new file mode 100644
index 0000000..ae986b0
--- /dev/null
+++ b/src/class04/Code05_SortArrayDistanceLessK.java
@@ -0,0 +1,127 @@
+package class04;
+
+import java.util.Arrays;
+import java.util.PriorityQueue;
+
+public class Code05_SortArrayDistanceLessK {
+
+	public static void sortedArrDistanceLessK(int[] arr, int k) {
+		if (k == 0) {
+			return;
+		}
+		// 默认小根堆
+		PriorityQueue<Integer> heap = new PriorityQueue<>();
+		int index = 0;
+		// 0...K-1
+		for (; index <= Math.min(arr.length - 1, k - 1); index++) {
+			heap.add(arr[index]);
+		}
+		int i = 0;
+		for (; index < arr.length; i++, index++) {
+			heap.add(arr[index]);
+			arr[i] = heap.poll();
+		}
+		while (!heap.isEmpty()) {
+			arr[i++] = heap.poll();
+		}
+	}
+
+	// for test
+	public static void comparator(int[] arr, int k) {
+		Arrays.sort(arr);
+	}
+
+	// for test
+	public static int[] randomArrayNoMoveMoreK(int maxSize, int maxValue, int K) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+		}
+		// 先排个序
+		Arrays.sort(arr);
+		// 然后开始随意交换，但是保证每个数距离不超过K
+		// swap[i] == true, 表示i位置已经参与过交换
+		// swap[i] == false, 表示i位置没有参与过交换
+		boolean[] isSwap = new boolean[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			int j = Math.min(i + (int) (Math.random() * (K + 1)), arr.length - 1);
+			if (!isSwap[i] && !isSwap[j]) {
+				isSwap[i] = true;
+				isSwap[j] = true;
+				int tmp = arr[i];
+				arr[i] = arr[j];
+				arr[j] = tmp;
+			}
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[] copyArray(int[] arr) {
+		if (arr == null) {
+			return null;
+		}
+		int[] res = new int[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			res[i] = arr[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static boolean isEqual(int[] arr1, int[] arr2) {
+		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
+			return false;
+		}
+		if (arr1 == null && arr2 == null) {
+			return true;
+		}
+		if (arr1.length != arr2.length) {
+			return false;
+		}
+		for (int i = 0; i < arr1.length; i++) {
+			if (arr1[i] != arr2[i]) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	// for test
+	public static void main(String[] args) {
+		System.out.println("test begin");
+		int testTime = 500000;
+		int maxSize = 100;
+		int maxValue = 100;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int k = (int) (Math.random() * maxSize) + 1;
+			int[] arr = randomArrayNoMoveMoreK(maxSize, maxValue, k);
+			int[] arr1 = copyArray(arr);
+			int[] arr2 = copyArray(arr);
+			sortedArrDistanceLessK(arr1, k);
+			comparator(arr2, k);
+			if (!isEqual(arr1, arr2)) {
+				succeed = false;
+				System.out.println("K : " + k);
+				printArray(arr);
+				printArray(arr1);
+				printArray(arr2);
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Fucking fucked!");
+	}
+
+}
\ No newline at end of file
diff --git a/src/class04/Test.java b/src/class04/Test.java
new file mode 100644
index 0000000..ce841f9
--- /dev/null
+++ b/src/class04/Test.java
@@ -0,0 +1,43 @@
+package class04;
+
+import java.util.Comparator;
+import java.util.PriorityQueue;
+
+
+public class Test {
+
+	//  负数，o1 放在上面的情况
+	public static class MyComp implements Comparator<Integer>{
+
+		@Override
+		public int compare(Integer o1, Integer o2) {
+			return o2 - o1;
+		}
+		
+	}
+	
+	
+	
+	public static void main(String[] args) {
+		System.out.println("hello");
+		// 大根堆
+		PriorityQueue<Integer> heap = new PriorityQueue<>(new MyComp());
+		
+		heap.add(5);
+		heap.add(7);
+		heap.add(3);
+		heap.add(0);
+		heap.add(2);
+		heap.add(5);
+		
+		while(!heap.isEmpty()) {
+			System.out.println(heap.poll());
+		}
+		
+		
+		
+		
+		
+	}
+	
+}
diff --git a/src/class05/Code01_TrieTree.java b/src/class05/Code01_TrieTree.java
new file mode 100644
index 0000000..fddcf13
--- /dev/null
+++ b/src/class05/Code01_TrieTree.java
@@ -0,0 +1,298 @@
+package class05;
+
+import java.util.HashMap;
+
+// 该程序的对数器跑不过，你能发现bug在哪吗？
+public class Code01_TrieTree {
+
+	public static class Node1 {
+		public int pass;
+		public int end;
+		public Node1[] nexts;
+
+		public Node1() {
+			pass = 0;
+			end = 0;
+			nexts = new Node1[26];
+		}
+	}
+
+	public static class Trie1 {
+		private Node1 root;
+
+		public Trie1() {
+			root = new Node1();
+		}
+
+		public void insert(String word) {
+			if (word == null) {
+				return;
+			}
+			char[] chs = word.toCharArray();
+			Node1 node = root;
+			node.pass++;
+			int index = 0;
+			for (int i = 0; i < chs.length; i++) { // 从左往右遍历字符
+				index = chs[i] - 'a'; // 由字符，对应成走向哪条路
+				if (node.nexts[index] == null) {
+					node.nexts[index] = new Node1();
+				}
+				node = node.nexts[index];
+				node.pass++;
+			}
+			node.end++;
+		}
+
+		public void delete(String word) {
+			if (search(word) != 0) {
+				char[] chs = word.toCharArray();
+				Node1 node = root;
+				node.pass--;
+				int index = 0;
+				for (int i = 0; i < chs.length; i++) {
+					index = chs[i] - 'a';
+					if (--node.nexts[index].pass == 0) {
+						node.nexts[index] = null;
+						return;
+					}
+					node = node.nexts[index];
+				}
+				node.end--;
+			}
+		}
+
+		// word这个单词之前加入过几次
+		public int search(String word) {
+			if (word == null) {
+				return 0;
+			}
+			char[] chs = word.toCharArray();
+			Node1 node = root;
+			int index = 0;
+			for (int i = 0; i < chs.length; i++) {
+				index = chs[i] - 'a';
+				if (node.nexts[index] == null) {
+					return 0;
+				}
+				node = node.nexts[index];
+			}
+			return node.end;
+		}
+
+		// 所有加入的字符串中，有几个是以pre这个字符串作为前缀的
+		public int prefixNumber(String pre) {
+			if (pre == null) {
+				return 0;
+			}
+			char[] chs = pre.toCharArray();
+			Node1 node = root;
+			int index = 0;
+			for (int i = 0; i < chs.length; i++) {
+				index = chs[i] - 'a';
+				if (node.nexts[index] == null) {
+					return 0;
+				}
+				node = node.nexts[index];
+			}
+			return node.pass;
+		}
+	}
+
+	public static class Node2 {
+		public int pass;
+		public int end;
+		public HashMap<Integer, Node2> nexts;
+
+		public Node2() {
+			pass = 0;
+			end = 0;
+			nexts = new HashMap<>();
+		}
+	}
+
+	public static class Trie2 {
+		private Node2 root;
+
+		public Trie2() {
+			root = new Node2();
+		}
+
+		public void insert(String word) {
+			if (word == null) {
+				return;
+			}
+			char[] chs = word.toCharArray();
+			Node2 node = root;
+			node.pass++;
+			int index = 0;
+			for (int i = 0; i < chs.length; i++) {
+				index = (int) chs[i];
+				if (!node.nexts.containsKey(index)) {
+					node.nexts.put(index, new Node2());
+				}
+				node = node.nexts.get(index);
+				node.pass++;
+			}
+			node.end++;
+		}
+
+		public void delete(String word) {
+			if (search(word) != 0) {
+				char[] chs = word.toCharArray();
+				Node2 node = root;
+				node.pass--;
+				int index = 0;
+				for (int i = 0; i < chs.length; i++) {
+					index = (int) chs[i];
+					if (--node.nexts.get(index).pass == 0) {
+						node.nexts.remove(index);
+						return;
+					}
+					node = node.nexts.get(index);
+				}
+				node.end--;
+			}
+		}
+
+		// word这个单词之前加入过几次
+		public int search(String word) {
+			if (word == null) {
+				return 0;
+			}
+			char[] chs = word.toCharArray();
+			Node2 node = root;
+			int index = 0;
+			for (int i = 0; i < chs.length; i++) {
+				index = (int) chs[i];
+				if (!node.nexts.containsKey(index)) {
+					return 0;
+				}
+				node = node.nexts.get(index);
+			}
+			return node.end;
+		}
+
+		// 所有加入的字符串中，有几个是以pre这个字符串作为前缀的
+		public int prefixNumber(String pre) {
+			if (pre == null) {
+				return 0;
+			}
+			char[] chs = pre.toCharArray();
+			Node2 node = root;
+			int index = 0;
+			for (int i = 0; i < chs.length; i++) {
+				index = (int) chs[i];
+				if (!node.nexts.containsKey(index)) {
+					return 0;
+				}
+				node = node.nexts.get(index);
+			}
+			return node.pass;
+		}
+	}
+
+	public static class Right {
+
+		private HashMap<String, Integer> box;
+
+		public Right() {
+			box = new HashMap<>();
+		}
+
+		public void insert(String word) {
+			if (!box.containsKey(word)) {
+				box.put(word, 1);
+			} else {
+				box.put(word, box.get(word) + 1);
+			}
+		}
+
+		public void delete(String word) {
+			if (box.containsKey(word)) {
+				if (box.get(word) == 1) {
+					box.remove(word);
+				} else {
+					box.put(word, box.get(word) - 1);
+				}
+			}
+		}
+
+		public int search(String word) {
+			if (!box.containsKey(word)) {
+				return 0;
+			} else {
+				return box.get(word);
+			}
+		}
+
+		public int prefixNumber(String pre) {
+			int count = 0;
+			for (String cur : box.keySet()) {
+				if (cur.startsWith(pre)) {
+					count++;
+				}
+			}
+			return count;
+		}
+	}
+
+	// for test
+	public static String generateRandomString(int strLen) {
+		char[] ans = new char[(int) (Math.random() * strLen) + 1];
+		for (int i = 0; i < ans.length; i++) {
+			int value = (int) (Math.random() * 6);
+			ans[i] = (char) (97 + value);
+		}
+		return String.valueOf(ans);
+	}
+
+	// for test
+	public static String[] generateRandomStringArray(int arrLen, int strLen) {
+		String[] ans = new String[(int) (Math.random() * arrLen) + 1];
+		for (int i = 0; i < ans.length; i++) {
+			ans[i] = generateRandomString(strLen);
+		}
+		return ans;
+	}
+
+	public static void main(String[] args) {
+		int arrLen = 100;
+		int strLen = 20;
+		int testTimes = 100000;
+		for (int i = 0; i < testTimes; i++) {
+			String[] arr = generateRandomStringArray(arrLen, strLen);
+			Trie1 trie1 = new Trie1();
+			Trie2 trie2 = new Trie2();
+			Right right = new Right();
+			for (int j = 0; j < arr.length; j++) {
+				double decide = Math.random();
+				if (decide < 0.25) {
+					trie1.insert(arr[j]);
+					trie2.insert(arr[j]);
+					right.insert(arr[j]);
+				} else if (decide < 0.5) {
+					trie1.delete(arr[j]);
+					trie2.delete(arr[j]);
+					right.delete(arr[j]);
+				} else if (decide < 0.75) {
+					int ans1 = trie1.search(arr[j]);
+					int ans2 = trie2.search(arr[j]);
+					int ans3 = right.search(arr[j]);
+					if (ans1 != ans2 || ans2 != ans3) {
+						System.out.println("Oops!");
+					}
+				} else {
+					int ans1 = trie1.prefixNumber(arr[j]);
+					int ans2 = trie2.prefixNumber(arr[j]);
+					int ans3 = right.prefixNumber(arr[j]);
+					if (ans1 != ans2 || ans2 != ans3) {
+						System.out.println("Oops!");
+					}
+				}
+			}
+		}
+		System.out.println("finish!");
+
+	}
+
+}
diff --git a/src/class05/Code02_TrieTree.java b/src/class05/Code02_TrieTree.java
new file mode 100644
index 0000000..a96cc5f
--- /dev/null
+++ b/src/class05/Code02_TrieTree.java
@@ -0,0 +1,305 @@
+package class05;
+
+import java.util.HashMap;
+
+// 该程序完全正确
+public class Code02_TrieTree {
+
+	public static class Node1 {
+		public int pass;
+		public int end;
+		public Node1[] nexts;
+
+		public Node1() {
+			pass = 0;
+			end = 0;
+			// 0    a
+			// 1    b
+			// 2    c
+			// ..   ..
+			// 25   z
+			// nexts[i] == null   i方向的路不存在
+			// nexts[i] != null   i方向的路存在
+			nexts = new Node1[26];
+		}
+	}
+
+	public static class Trie1 {
+		private Node1 root;
+
+		public Trie1() {
+			root = new Node1();
+		}
+
+		public void insert(String word) {
+			if (word == null) {
+				return;
+			}
+			char[] str = word.toCharArray();
+			Node1 node = root;
+			node.pass++;
+			int path = 0;
+			for (int i = 0; i < str.length; i++) { // 从左往右遍历字符
+				path = str[i] - 'a'; // 由字符，对应成走向哪条路
+				if (node.nexts[path] == null) {
+					node.nexts[path] = new Node1();
+				}
+				node = node.nexts[path];
+				node.pass++;
+			}
+			node.end++;
+		}
+
+		public void delete(String word) {
+			if (search(word) != 0) {
+				char[] chs = word.toCharArray();
+				Node1 node = root;
+				node.pass--;
+				int path = 0;
+				for (int i = 0; i < chs.length; i++) {
+					path = chs[i] - 'a';
+					if (--node.nexts[path].pass == 0) {
+						node.nexts[path] = null;
+						return;
+					}
+					node = node.nexts[path];
+				}
+				node.end--;
+			}
+		}
+
+		// word这个单词之前加入过几次
+		public int search(String word) {
+			if (word == null) {
+				return 0;
+			}
+			char[] chs = word.toCharArray();
+			Node1 node = root;
+			int index = 0;
+			for (int i = 0; i < chs.length; i++) {
+				index = chs[i] - 'a';
+				if (node.nexts[index] == null) {
+					return 0;
+				}
+				node = node.nexts[index];
+			}
+			return node.end;
+		}
+
+		// 所有加入的字符串中，有几个是以pre这个字符串作为前缀的
+		public int prefixNumber(String pre) {
+			if (pre == null) {
+				return 0;
+			}
+			char[] chs = pre.toCharArray();
+			Node1 node = root;
+			int index = 0;
+			for (int i = 0; i < chs.length; i++) {
+				index = chs[i] - 'a';
+				if (node.nexts[index] == null) {
+					return 0;
+				}
+				node = node.nexts[index];
+			}
+			return node.pass;
+		}
+	}
+
+	public static class Node2 {
+		public int pass;
+		public int end;
+		public HashMap<Integer, Node2> nexts;
+
+		public Node2() {
+			pass = 0;
+			end = 0;
+			nexts = new HashMap<>();
+		}
+	}
+
+	public static class Trie2 {
+		private Node2 root;
+
+		public Trie2() {
+			root = new Node2();
+		}
+
+		public void insert(String word) {
+			if (word == null) {
+				return;
+			}
+			char[] chs = word.toCharArray();
+			Node2 node = root;
+			node.pass++;
+			int index = 0;
+			for (int i = 0; i < chs.length; i++) {
+				index = (int) chs[i];
+				if (!node.nexts.containsKey(index)) {
+					node.nexts.put(index, new Node2());
+				}
+				node = node.nexts.get(index);
+				node.pass++;
+			}
+			node.end++;
+		}
+
+		public void delete(String word) {
+			if (search(word) != 0) {
+				char[] chs = word.toCharArray();
+				Node2 node = root;
+				node.pass--;
+				int index = 0;
+				for (int i = 0; i < chs.length; i++) {
+					index = (int) chs[i];
+					if (--node.nexts.get(index).pass == 0) {
+						node.nexts.remove(index);
+						return;
+					}
+					node = node.nexts.get(index);
+				}
+				node.end--;
+			}
+		}
+
+		// word这个单词之前加入过几次
+		public int search(String word) {
+			if (word == null) {
+				return 0;
+			}
+			char[] chs = word.toCharArray();
+			Node2 node = root;
+			int index = 0;
+			for (int i = 0; i < chs.length; i++) {
+				index = (int) chs[i];
+				if (!node.nexts.containsKey(index)) {
+					return 0;
+				}
+				node = node.nexts.get(index);
+			}
+			return node.end;
+		}
+
+		// 所有加入的字符串中，有几个是以pre这个字符串作为前缀的
+		public int prefixNumber(String pre) {
+			if (pre == null) {
+				return 0;
+			}
+			char[] chs = pre.toCharArray();
+			Node2 node = root;
+			int index = 0;
+			for (int i = 0; i < chs.length; i++) {
+				index = (int) chs[i];
+				if (!node.nexts.containsKey(index)) {
+					return 0;
+				}
+				node = node.nexts.get(index);
+			}
+			return node.pass;
+		}
+	}
+
+	public static class Right {
+
+		private HashMap<String, Integer> box;
+
+		public Right() {
+			box = new HashMap<>();
+		}
+
+		public void insert(String word) {
+			if (!box.containsKey(word)) {
+				box.put(word, 1);
+			} else {
+				box.put(word, box.get(word) + 1);
+			}
+		}
+
+		public void delete(String word) {
+			if (box.containsKey(word)) {
+				if (box.get(word) == 1) {
+					box.remove(word);
+				} else {
+					box.put(word, box.get(word) - 1);
+				}
+			}
+		}
+
+		public int search(String word) {
+			if (!box.containsKey(word)) {
+				return 0;
+			} else {
+				return box.get(word);
+			}
+		}
+
+		public int prefixNumber(String pre) {
+			int count = 0;
+			for (String cur : box.keySet()) {
+				if (cur.startsWith(pre)) {
+					count += box.get(cur);
+				}
+			}
+			return count;
+		}
+	}
+
+	// for test
+	public static String generateRandomString(int strLen) {
+		char[] ans = new char[(int) (Math.random() * strLen) + 1];
+		for (int i = 0; i < ans.length; i++) {
+			int value = (int) (Math.random() * 6);
+			ans[i] = (char) (97 + value);
+		}
+		return String.valueOf(ans);
+	}
+
+	// for test
+	public static String[] generateRandomStringArray(int arrLen, int strLen) {
+		String[] ans = new String[(int) (Math.random() * arrLen) + 1];
+		for (int i = 0; i < ans.length; i++) {
+			ans[i] = generateRandomString(strLen);
+		}
+		return ans;
+	}
+
+	public static void main(String[] args) {
+		int arrLen = 100;
+		int strLen = 20;
+		int testTimes = 100000;
+		for (int i = 0; i < testTimes; i++) {
+			String[] arr = generateRandomStringArray(arrLen, strLen);
+			Trie1 trie1 = new Trie1();
+			Trie2 trie2 = new Trie2();
+			Right right = new Right();
+			for (int j = 0; j < arr.length; j++) {
+				double decide = Math.random();
+				if (decide < 0.25) {
+					trie1.insert(arr[j]);
+					trie2.insert(arr[j]);
+					right.insert(arr[j]);
+				} else if (decide < 0.5) {
+					trie1.delete(arr[j]);
+					trie2.delete(arr[j]);
+					right.delete(arr[j]);
+				} else if (decide < 0.75) {
+					int ans1 = trie1.search(arr[j]);
+					int ans2 = trie2.search(arr[j]);
+					int ans3 = right.search(arr[j]);
+					if (ans1 != ans2 || ans2 != ans3) {
+						System.out.println("Oops!");
+					}
+				} else {
+					int ans1 = trie1.prefixNumber(arr[j]);
+					int ans2 = trie2.prefixNumber(arr[j]);
+					int ans3 = right.prefixNumber(arr[j]);
+					if (ans1 != ans2 || ans2 != ans3) {
+						System.out.println("Oops!");
+					}
+				}
+			}
+		}
+		System.out.println("finish!");
+
+	}
+
+}
diff --git a/src/class05/Code03_CountSort.java b/src/class05/Code03_CountSort.java
new file mode 100644
index 0000000..0f64d1c
--- /dev/null
+++ b/src/class05/Code03_CountSort.java
@@ -0,0 +1,111 @@
+package class05;
+
+import java.util.Arrays;
+
+public class Code03_CountSort {
+
+	// only for 0~200 value
+	public static void countSort(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return;
+		}
+		int max = Integer.MIN_VALUE;
+		for (int i = 0; i < arr.length; i++) {
+			max = Math.max(max, arr[i]);
+		}
+		int[] bucket = new int[max + 1];
+		for (int i = 0; i < arr.length; i++) {
+			bucket[arr[i]]++;
+		}
+		int i = 0;
+		for (int j = 0; j < bucket.length; j++) {
+			while (bucket[j]-- > 0) {
+				arr[i++] = j;
+			}
+		}
+	}
+
+	// for test
+	public static void comparator(int[] arr) {
+		Arrays.sort(arr);
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random());
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[] copyArray(int[] arr) {
+		if (arr == null) {
+			return null;
+		}
+		int[] res = new int[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			res[i] = arr[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static boolean isEqual(int[] arr1, int[] arr2) {
+		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
+			return false;
+		}
+		if (arr1 == null && arr2 == null) {
+			return true;
+		}
+		if (arr1.length != arr2.length) {
+			return false;
+		}
+		for (int i = 0; i < arr1.length; i++) {
+			if (arr1[i] != arr2[i]) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	// for test
+	public static void main(String[] args) {
+		int testTime = 500000;
+		int maxSize = 100;
+		int maxValue = 150;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr1 = generateRandomArray(maxSize, maxValue);
+			int[] arr2 = copyArray(arr1);
+			countSort(arr1);
+			comparator(arr2);
+			if (!isEqual(arr1, arr2)) {
+				succeed = false;
+				printArray(arr1);
+				printArray(arr2);
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Fucking fucked!");
+
+		int[] arr = generateRandomArray(maxSize, maxValue);
+		printArray(arr);
+		countSort(arr);
+		printArray(arr);
+
+	}
+
+}
diff --git a/src/class05/Code04_RadixSort.java b/src/class05/Code04_RadixSort.java
new file mode 100644
index 0000000..325d97b
--- /dev/null
+++ b/src/class05/Code04_RadixSort.java
@@ -0,0 +1,153 @@
+package class05;
+
+import java.util.Arrays;
+
+public class Code04_RadixSort {
+
+	// only for no-negative value
+	public static void radixSort(int[] arr) {
+		if (arr == null || arr.length < 2) {
+			return;
+		}
+		radixSort(arr, 0, arr.length - 1, maxbits(arr));
+	}
+
+	public static int maxbits(int[] arr) {
+		int max = Integer.MIN_VALUE;
+		for (int i = 0; i < arr.length; i++) {
+			max = Math.max(max, arr[i]);
+		}
+		int res = 0;
+		while (max != 0) {
+			res++;
+			max /= 10;
+		}
+		return res;
+	}
+
+	// arr[l..r]排序  ,  digit
+	// l..r    3 56 17 100    3
+	public static void radixSort(int[] arr, int L, int R, int digit) {
+		final int radix = 10;
+		int i = 0, j = 0;
+		// 有多少个数准备多少个辅助空间
+		int[] help = new int[R - L + 1];
+		for (int d = 1; d <= digit; d++) { // 有多少位就进出几次
+			// 10个空间
+		    // count[0] 当前位(d位)是0的数字有多少个
+			// count[1] 当前位(d位)是(0和1)的数字有多少个
+			// count[2] 当前位(d位)是(0、1和2)的数字有多少个
+			// count[i] 当前位(d位)是(0~i)的数字有多少个
+			int[] count = new int[radix]; // count[0..9]
+			for (i = L; i <= R; i++) {
+				// 103  1   3
+				// 209  1   9
+				j = getDigit(arr[i], d);
+				count[j]++;
+			}
+			for (i = 1; i < radix; i++) {
+				count[i] = count[i] + count[i - 1];
+			}
+			for (i = R; i >= L; i--) {
+				j = getDigit(arr[i], d);
+				help[count[j] - 1] = arr[i];
+				count[j]--;
+			}
+			for (i = L, j = 0; i <= R; i++, j++) {
+				arr[i] = help[j];
+			}
+		}
+		
+		
+		
+		
+	}
+
+	public static int getDigit(int x, int d) {
+		return ((x / ((int) Math.pow(10, d - 1))) % 10);
+	}
+
+	// for test
+	public static void comparator(int[] arr) {
+		Arrays.sort(arr);
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random());
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[] copyArray(int[] arr) {
+		if (arr == null) {
+			return null;
+		}
+		int[] res = new int[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			res[i] = arr[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static boolean isEqual(int[] arr1, int[] arr2) {
+		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
+			return false;
+		}
+		if (arr1 == null && arr2 == null) {
+			return true;
+		}
+		if (arr1.length != arr2.length) {
+			return false;
+		}
+		for (int i = 0; i < arr1.length; i++) {
+			if (arr1[i] != arr2[i]) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr == null) {
+			return;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	// for test
+	public static void main(String[] args) {
+		int testTime = 500000;
+		int maxSize = 100;
+		int maxValue = 100000;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr1 = generateRandomArray(maxSize, maxValue);
+			int[] arr2 = copyArray(arr1);
+			radixSort(arr1);
+			comparator(arr2);
+			if (!isEqual(arr1, arr2)) {
+				succeed = false;
+				printArray(arr1);
+				printArray(arr2);
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Fucking fucked!");
+
+		int[] arr = generateRandomArray(maxSize, maxValue);
+		printArray(arr);
+		radixSort(arr);
+		printArray(arr);
+
+	}
+
+}
diff --git a/src/class06/Code01_LinkedListMid.java b/src/class06/Code01_LinkedListMid.java
new file mode 100644
index 0000000..04cc571
--- /dev/null
+++ b/src/class06/Code01_LinkedListMid.java
@@ -0,0 +1,162 @@
+package class06;
+
+import java.util.ArrayList;
+
+public class Code01_LinkedListMid {
+
+	public static class Node {
+		public int value;
+		public Node next;
+
+		public Node(int v) {
+			value = v;
+		}
+	}
+
+	// head 头
+	public static Node midOrUpMidNode(Node head) {
+		if (head == null || head.next == null || head.next.next == null) {
+			return head;
+		}
+		// 链表有3个点或以上
+		Node slow = head.next;
+		Node fast = head.next.next;
+		while (fast.next != null && fast.next.next != null) {
+			slow = slow.next;
+			fast = fast.next.next;
+		}
+		return slow;
+	}
+
+	public static Node midOrDownMidNode(Node head) {
+		if (head == null || head.next == null) {
+			return head;
+		}
+		Node slow = head.next;
+		Node fast = head.next;
+		while (fast.next != null && fast.next.next != null) {
+			slow = slow.next;
+			fast = fast.next.next;
+		}
+		return slow;
+	}
+
+	public static Node midOrUpMidPreNode(Node head) {
+		if (head == null || head.next == null || head.next.next == null) {
+			return null;
+		}
+		Node slow = head;
+		Node fast = head.next.next;
+		while (fast.next != null && fast.next.next != null) {
+			slow = slow.next;
+			fast = fast.next.next;
+		}
+		return slow;
+	}
+
+	public static Node midOrDownMidPreNode(Node head) {
+		if (head == null || head.next == null) {
+			return null;
+		}
+		if (head.next.next == null) {
+			return head;
+		}
+		Node slow = head;
+		Node fast = head.next;
+		while (fast.next != null && fast.next.next != null) {
+			slow = slow.next;
+			fast = fast.next.next;
+		}
+		return slow;
+	}
+
+	public static Node right1(Node head) {
+		if (head == null) {
+			return null;
+		}
+		Node cur = head;
+		ArrayList<Node> arr = new ArrayList<>();
+		while (cur != null) {
+			arr.add(cur);
+			cur = cur.next;
+		}
+		return arr.get((arr.size() - 1) / 2);
+	}
+
+	public static Node right2(Node head) {
+		if (head == null) {
+			return null;
+		}
+		Node cur = head;
+		ArrayList<Node> arr = new ArrayList<>();
+		while (cur != null) {
+			arr.add(cur);
+			cur = cur.next;
+		}
+		return arr.get(arr.size() / 2);
+	}
+
+	public static Node right3(Node head) {
+		if (head == null || head.next == null || head.next.next == null) {
+			return null;
+		}
+		Node cur = head;
+		ArrayList<Node> arr = new ArrayList<>();
+		while (cur != null) {
+			arr.add(cur);
+			cur = cur.next;
+		}
+		return arr.get((arr.size() - 3) / 2);
+	}
+
+	public static Node right4(Node head) {
+		if (head == null || head.next == null) {
+			return null;
+		}
+		Node cur = head;
+		ArrayList<Node> arr = new ArrayList<>();
+		while (cur != null) {
+			arr.add(cur);
+			cur = cur.next;
+		}
+		return arr.get((arr.size() - 2) / 2);
+	}
+
+	public static void main(String[] args) {
+		Node test = null;
+		test = new Node(0);
+		test.next = new Node(1);
+		test.next.next = new Node(2);
+		test.next.next.next = new Node(3);
+		test.next.next.next.next = new Node(4);
+		test.next.next.next.next.next = new Node(5);
+		test.next.next.next.next.next.next = new Node(6);
+		test.next.next.next.next.next.next.next = new Node(7);
+		test.next.next.next.next.next.next.next.next = new Node(8);
+
+		Node ans1 = null;
+		Node ans2 = null;
+
+		ans1 = midOrUpMidNode(test);
+		ans2 = right1(test);
+		System.out.println(ans1 != null ? ans1.value : "无");
+		System.out.println(ans2 != null ? ans2.value : "无");
+
+		ans1 = midOrDownMidNode(test);
+		ans2 = right2(test);
+		System.out.println(ans1 != null ? ans1.value : "无");
+		System.out.println(ans2 != null ? ans2.value : "无");
+
+		ans1 = midOrUpMidPreNode(test);
+		ans2 = right3(test);
+		System.out.println(ans1 != null ? ans1.value : "无");
+		System.out.println(ans2 != null ? ans2.value : "无");
+
+		ans1 = midOrDownMidPreNode(test);
+		ans2 = right4(test);
+		System.out.println(ans1 != null ? ans1.value : "无");
+		System.out.println(ans2 != null ? ans2.value : "无");
+
+	}
+
+}
diff --git a/src/class06/Code02_IsPalindromeList.java b/src/class06/Code02_IsPalindromeList.java
new file mode 100644
index 0000000..090409d
--- /dev/null
+++ b/src/class06/Code02_IsPalindromeList.java
@@ -0,0 +1,204 @@
+package class06;
+
+import java.util.Stack;
+
+public class Code02_IsPalindromeList {
+
+	public static class Node {
+		public int value;
+		public Node next;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	// need n extra space
+	public static boolean isPalindrome1(Node head) {
+		Stack<Node> stack = new Stack<Node>();
+		Node cur = head;
+		while (cur != null) {
+			stack.push(cur);
+			cur = cur.next;
+		}
+		while (head != null) {
+			if (head.value != stack.pop().value) {
+				return false;
+			}
+			head = head.next;
+		}
+		return true;
+	}
+
+	// need n/2 extra space
+	public static boolean isPalindrome2(Node head) {
+		if (head == null || head.next == null) {
+			return true;
+		}
+		Node right = head.next;
+		Node cur = head;
+		while (cur.next != null && cur.next.next != null) {
+			right = right.next;
+			cur = cur.next.next;
+		}
+		Stack<Node> stack = new Stack<Node>();
+		while (right != null) {
+			stack.push(right);
+			right = right.next;
+		}
+		while (!stack.isEmpty()) {
+			if (head.value != stack.pop().value) {
+				return false;
+			}
+			head = head.next;
+		}
+		return true;
+	}
+
+	// need O(1) extra space
+	public static boolean isPalindrome3(Node head) {
+		if (head == null || head.next == null) {
+			return true;
+		}
+		Node n1 = head;
+		Node n2 = head;
+		while (n2.next != null && n2.next.next != null) { // find mid node
+			n1 = n1.next; // n1 -> mid
+			n2 = n2.next.next; // n2 -> end
+		}
+		// n1 中点
+		
+		
+		n2 = n1.next; // n2 -> right part first node
+		n1.next = null; // mid.next -> null
+		Node n3 = null;
+		while (n2 != null) { // right part convert
+			n3 = n2.next; // n3 -> save next node
+			n2.next = n1; // next of right node convert
+			n1 = n2; // n1 move
+			n2 = n3; // n2 move
+		}
+		n3 = n1; // n3 -> save last node
+		n2 = head;// n2 -> left first node
+		boolean res = true;
+		while (n1 != null && n2 != null) { // check palindrome
+			if (n1.value != n2.value) {
+				res = false;
+				break;
+			}
+			n1 = n1.next; // left to mid
+			n2 = n2.next; // right to mid
+		}
+		n1 = n3.next;
+		n3.next = null;
+		while (n1 != null) { // recover list
+			n2 = n1.next;
+			n1.next = n3;
+			n3 = n1;
+			n1 = n2;
+		}
+		return res;
+	}
+
+	public static void printLinkedList(Node node) {
+		System.out.print("Linked List: ");
+		while (node != null) {
+			System.out.print(node.value + " ");
+			node = node.next;
+		}
+		System.out.println();
+	}
+
+	public static void main(String[] args) {
+
+		Node head = null;
+		printLinkedList(head);
+		System.out.print(isPalindrome1(head) + " | ");
+		System.out.print(isPalindrome2(head) + " | ");
+		System.out.println(isPalindrome3(head) + " | ");
+		printLinkedList(head);
+		System.out.println("=========================");
+
+		head = new Node(1);
+		printLinkedList(head);
+		System.out.print(isPalindrome1(head) + " | ");
+		System.out.print(isPalindrome2(head) + " | ");
+		System.out.println(isPalindrome3(head) + " | ");
+		printLinkedList(head);
+		System.out.println("=========================");
+
+		head = new Node(1);
+		head.next = new Node(2);
+		printLinkedList(head);
+		System.out.print(isPalindrome1(head) + " | ");
+		System.out.print(isPalindrome2(head) + " | ");
+		System.out.println(isPalindrome3(head) + " | ");
+		printLinkedList(head);
+		System.out.println("=========================");
+
+		head = new Node(1);
+		head.next = new Node(1);
+		printLinkedList(head);
+		System.out.print(isPalindrome1(head) + " | ");
+		System.out.print(isPalindrome2(head) + " | ");
+		System.out.println(isPalindrome3(head) + " | ");
+		printLinkedList(head);
+		System.out.println("=========================");
+
+		head = new Node(1);
+		head.next = new Node(2);
+		head.next.next = new Node(3);
+		printLinkedList(head);
+		System.out.print(isPalindrome1(head) + " | ");
+		System.out.print(isPalindrome2(head) + " | ");
+		System.out.println(isPalindrome3(head) + " | ");
+		printLinkedList(head);
+		System.out.println("=========================");
+
+		head = new Node(1);
+		head.next = new Node(2);
+		head.next.next = new Node(1);
+		printLinkedList(head);
+		System.out.print(isPalindrome1(head) + " | ");
+		System.out.print(isPalindrome2(head) + " | ");
+		System.out.println(isPalindrome3(head) + " | ");
+		printLinkedList(head);
+		System.out.println("=========================");
+
+		head = new Node(1);
+		head.next = new Node(2);
+		head.next.next = new Node(3);
+		head.next.next.next = new Node(1);
+		printLinkedList(head);
+		System.out.print(isPalindrome1(head) + " | ");
+		System.out.print(isPalindrome2(head) + " | ");
+		System.out.println(isPalindrome3(head) + " | ");
+		printLinkedList(head);
+		System.out.println("=========================");
+
+		head = new Node(1);
+		head.next = new Node(2);
+		head.next.next = new Node(2);
+		head.next.next.next = new Node(1);
+		printLinkedList(head);
+		System.out.print(isPalindrome1(head) + " | ");
+		System.out.print(isPalindrome2(head) + " | ");
+		System.out.println(isPalindrome3(head) + " | ");
+		printLinkedList(head);
+		System.out.println("=========================");
+
+		head = new Node(1);
+		head.next = new Node(2);
+		head.next.next = new Node(3);
+		head.next.next.next = new Node(2);
+		head.next.next.next.next = new Node(1);
+		printLinkedList(head);
+		System.out.print(isPalindrome1(head) + " | ");
+		System.out.print(isPalindrome2(head) + " | ");
+		System.out.println(isPalindrome3(head) + " | ");
+		printLinkedList(head);
+		System.out.println("=========================");
+
+	}
+
+}
diff --git a/src/class06/Code03_SmallerEqualBigger.java b/src/class06/Code03_SmallerEqualBigger.java
new file mode 100644
index 0000000..d234365
--- /dev/null
+++ b/src/class06/Code03_SmallerEqualBigger.java
@@ -0,0 +1,136 @@
+package class06;
+
+public class Code03_SmallerEqualBigger {
+
+	public static class Node {
+		public int value;
+		public Node next;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static Node listPartition1(Node head, int pivot) {
+		if (head == null) {
+			return head;
+		}
+		Node cur = head;
+		int i = 0;
+		while (cur != null) {
+			i++;
+			cur = cur.next;
+		}
+		Node[] nodeArr = new Node[i];
+		i = 0;
+		cur = head;
+		for (i = 0; i != nodeArr.length; i++) {
+			nodeArr[i] = cur;
+			cur = cur.next;
+		}
+		arrPartition(nodeArr, pivot);
+		for (i = 1; i != nodeArr.length; i++) {
+			nodeArr[i - 1].next = nodeArr[i];
+		}
+		nodeArr[i - 1].next = null;
+		return nodeArr[0];
+	}
+
+	public static void arrPartition(Node[] nodeArr, int pivot) {
+		int small = -1;
+		int big = nodeArr.length;
+		int index = 0;
+		while (index != big) {
+			if (nodeArr[index].value < pivot) {
+				swap(nodeArr, ++small, index++);
+			} else if (nodeArr[index].value == pivot) {
+				index++;
+			} else {
+				swap(nodeArr, --big, index);
+			}
+		}
+	}
+
+	public static void swap(Node[] nodeArr, int a, int b) {
+		Node tmp = nodeArr[a];
+		nodeArr[a] = nodeArr[b];
+		nodeArr[b] = tmp;
+	}
+
+	public static Node listPartition2(Node head, int pivot) {
+		Node sH = null; // small head
+		Node sT = null; // small tail
+		Node eH = null; // equal head
+		Node eT = null; // equal tail
+		Node mH = null; // big head
+		Node mT = null; // big tail
+		Node next = null; // save next node
+		// every node distributed to three lists
+		while (head != null) {
+			next = head.next;
+			head.next = null;
+			if (head.value < pivot) {
+				if (sH == null) {
+					sH = head;
+					sT = head;
+				} else {
+					sT.next = head;
+					sT = head;
+				}
+			} else if (head.value == pivot) {
+				if (eH == null) {
+					eH = head;
+					eT = head;
+				} else {
+					eT.next = head;
+					eT = head;
+				}
+			} else {
+				if (mH == null) {
+					mH = head;
+					mT = head;
+				} else {
+					mT.next = head;
+					mT = head;
+				}
+			}
+			head = next;
+		}
+		// 小于区域的尾巴，连等于区域的头，等于区域的尾巴连大于区域的头
+		if (sT != null) { // 如果有小于区域
+			sT.next = eH;
+			eT = eT == null ? sT : eT; // 下一步，谁去连大于区域的头，谁就变成eT
+		}
+		// 上面的if，不管跑了没有，et
+		// all reconnect
+		if (eT != null) { // 如果小于区域和等于区域，不是都没有
+			eT.next = mH;
+		}
+		return sH != null ? sH : (eH != null ? eH : mH);
+	}
+
+	public static void printLinkedList(Node node) {
+		System.out.print("Linked List: ");
+		while (node != null) {
+			System.out.print(node.value + " ");
+			node = node.next;
+		}
+		System.out.println();
+	}
+
+	public static void main(String[] args) {
+		Node head1 = new Node(7);
+		head1.next = new Node(9);
+		head1.next.next = new Node(1);
+		head1.next.next.next = new Node(8);
+		head1.next.next.next.next = new Node(5);
+		head1.next.next.next.next.next = new Node(2);
+		head1.next.next.next.next.next.next = new Node(5);
+		printLinkedList(head1);
+		// head1 = listPartition1(head1, 4);
+		head1 = listPartition2(head1, 5);
+		printLinkedList(head1);
+
+	}
+
+}
diff --git a/src/class06/Code04_CopyListWithRandom.java b/src/class06/Code04_CopyListWithRandom.java
new file mode 100644
index 0000000..be21b71
--- /dev/null
+++ b/src/class06/Code04_CopyListWithRandom.java
@@ -0,0 +1,130 @@
+package class06;
+
+import java.util.HashMap;
+
+public class Code04_CopyListWithRandom {
+
+	public static class Node {
+		public int value;
+		public Node next;
+		public Node rand;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static Node copyListWithRand1(Node head) {
+		HashMap<Node, Node> map = new HashMap<Node, Node>();
+		Node cur = head;
+		while (cur != null) {
+			map.put(cur, new Node(cur.value));
+			cur = cur.next;
+		}
+		cur = head;
+		while (cur != null) {
+			// cur 老
+			// map.get(cur) 新
+			map.get(cur).next = map.get(cur.next);
+			map.get(cur).rand = map.get(cur.rand);
+			cur = cur.next;
+		}
+		return map.get(head);
+	}
+
+	public static Node copyListWithRand2(Node head) {
+		if (head == null) {
+			return null;
+		}
+		Node cur = head;
+		Node next = null;
+		// copy node and link to every node
+		// 1 -> 2
+		// 1 -> 1' -> 2
+		while (cur != null) {
+			// cur 老   next 老的下一个
+			next = cur.next;
+			cur.next = new Node(cur.value);
+			cur.next.next = next;
+			cur = next;
+		}
+		cur = head;
+		Node curCopy = null;
+		// set copy node rand
+		// 1 -> 1' -> 2 -> 2'
+		while (cur != null) {
+			// cur 老
+			// cur.next  新 copy
+			next = cur.next.next;
+			curCopy = cur.next;
+			curCopy.rand = cur.rand != null ? cur.rand.next : null;
+			cur = next;
+		}
+		// head  head.next
+		Node res = head.next;
+		cur = head;
+		// split
+		while (cur != null) {
+			next = cur.next.next;
+			curCopy = cur.next;
+			cur.next = next;
+			curCopy.next = next != null ? next.next : null;
+			cur = next;
+		}
+		return res;
+	}
+
+	public static void printRandLinkedList(Node head) {
+		Node cur = head;
+		System.out.print("order: ");
+		while (cur != null) {
+			System.out.print(cur.value + " ");
+			cur = cur.next;
+		}
+		System.out.println();
+		cur = head;
+		System.out.print("rand:  ");
+		while (cur != null) {
+			System.out.print(cur.rand == null ? "- " : cur.rand.value + " ");
+			cur = cur.next;
+		}
+		System.out.println();
+	}
+
+	public static void main(String[] args) {
+		Node head = null;
+		Node res1 = null;
+		Node res2 = null;
+		printRandLinkedList(head);
+		res1 = copyListWithRand1(head);
+		printRandLinkedList(res1);
+		res2 = copyListWithRand2(head);
+		printRandLinkedList(res2);
+		printRandLinkedList(head);
+		System.out.println("=========================");
+
+		head = new Node(1);
+		head.next = new Node(2);
+		head.next.next = new Node(3);
+		head.next.next.next = new Node(4);
+		head.next.next.next.next = new Node(5);
+		head.next.next.next.next.next = new Node(6);
+
+		head.rand = head.next.next.next.next.next; // 1 -> 6
+		head.next.rand = head.next.next.next.next.next; // 2 -> 6
+		head.next.next.rand = head.next.next.next.next; // 3 -> 5
+		head.next.next.next.rand = head.next.next; // 4 -> 3
+		head.next.next.next.next.rand = null; // 5 -> null
+		head.next.next.next.next.next.rand = head.next.next.next; // 6 -> 4
+
+		printRandLinkedList(head);
+		res1 = copyListWithRand1(head);
+		printRandLinkedList(res1);
+		res2 = copyListWithRand2(head);
+		printRandLinkedList(res2);
+		printRandLinkedList(head);
+		System.out.println("=========================");
+
+	}
+
+}
diff --git a/src/class06/Code05_FindFirstIntersectNode.java b/src/class06/Code05_FindFirstIntersectNode.java
new file mode 100644
index 0000000..40eb34e
--- /dev/null
+++ b/src/class06/Code05_FindFirstIntersectNode.java
@@ -0,0 +1,169 @@
+package class06;
+
+public class Code05_FindFirstIntersectNode {
+
+	public static class Node {
+		public int value;
+		public Node next;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static Node getIntersectNode(Node head1, Node head2) {
+		if (head1 == null || head2 == null) {
+			return null;
+		}
+		Node loop1 = getLoopNode(head1);
+		Node loop2 = getLoopNode(head2);
+		if (loop1 == null && loop2 == null) {
+			return noLoop(head1, head2);
+		}
+		if (loop1 != null && loop2 != null) {
+			return bothLoop(head1, loop1, head2, loop2);
+		}
+		return null;
+	}
+
+	// 找到链表第一个入环节点，如果无环，返回null
+	public static Node getLoopNode(Node head) {
+		if (head == null || head.next == null || head.next.next == null) {
+			return null;
+		}
+		// n1 慢  n2 快
+		Node n1 = head.next; // n1 -> slow
+		Node n2 = head.next.next; // n2 -> fast
+		while (n1 != n2) {
+			if (n2.next == null || n2.next.next == null) {
+				return null;
+			}
+			n2 = n2.next.next;
+			n1 = n1.next;
+		}
+		n2 = head; // n2 -> walk again from head
+		while (n1 != n2) {
+			n1 = n1.next;
+			n2 = n2.next;
+		}
+		return n1;
+	}
+
+	// 如果两个链表都无环，返回第一个相交节点，如果不想交，返回null
+	public static Node noLoop(Node head1, Node head2) {
+		if (head1 == null || head2 == null) {
+			return null;
+		}
+		Node cur1 = head1;
+		Node cur2 = head2;
+		int n = 0;
+		while (cur1.next != null) {
+			n++;
+			cur1 = cur1.next;
+		}
+		while (cur2.next != null) {
+			n--;
+			cur2 = cur2.next;
+		}
+		if (cur1 != cur2) {
+			return null;
+		}
+		// n  :  链表1长度减去链表2长度的值
+		cur1 = n > 0 ? head1 : head2; // 谁长，谁的头变成cur1
+		cur2 = cur1 == head1 ? head2 : head1; // 谁短，谁的头变成cur2
+		n = Math.abs(n);
+		while (n != 0) {
+			n--;
+			cur1 = cur1.next;
+		}
+		while (cur1 != cur2) {
+			cur1 = cur1.next;
+			cur2 = cur2.next;
+		}
+		return cur1;
+	}
+
+	// 两个有环链表，返回第一个相交节点，如果不想交返回null
+	public static Node bothLoop(Node head1, Node loop1, Node head2, Node loop2) {
+		Node cur1 = null;
+		Node cur2 = null;
+		if (loop1 == loop2) {
+			cur1 = head1;
+			cur2 = head2;
+			int n = 0;
+			while (cur1 != loop1) {
+				n++;
+				cur1 = cur1.next;
+			}
+			while (cur2 != loop2) {
+				n--;
+				cur2 = cur2.next;
+			}
+			cur1 = n > 0 ? head1 : head2;
+			cur2 = cur1 == head1 ? head2 : head1;
+			n = Math.abs(n);
+			while (n != 0) {
+				n--;
+				cur1 = cur1.next;
+			}
+			while (cur1 != cur2) {
+				cur1 = cur1.next;
+				cur2 = cur2.next;
+			}
+			return cur1;
+		} else {
+			cur1 = loop1.next;
+			while (cur1 != loop1) {
+				if (cur1 == loop2) {
+					return loop1;
+				}
+				cur1 = cur1.next;
+			}
+			return null;
+		}
+	}
+
+	public static void main(String[] args) {
+		// 1->2->3->4->5->6->7->null
+		Node head1 = new Node(1);
+		head1.next = new Node(2);
+		head1.next.next = new Node(3);
+		head1.next.next.next = new Node(4);
+		head1.next.next.next.next = new Node(5);
+		head1.next.next.next.next.next = new Node(6);
+		head1.next.next.next.next.next.next = new Node(7);
+
+		// 0->9->8->6->7->null
+		Node head2 = new Node(0);
+		head2.next = new Node(9);
+		head2.next.next = new Node(8);
+		head2.next.next.next = head1.next.next.next.next.next; // 8->6
+		System.out.println(getIntersectNode(head1, head2).value);
+
+		// 1->2->3->4->5->6->7->4...
+		head1 = new Node(1);
+		head1.next = new Node(2);
+		head1.next.next = new Node(3);
+		head1.next.next.next = new Node(4);
+		head1.next.next.next.next = new Node(5);
+		head1.next.next.next.next.next = new Node(6);
+		head1.next.next.next.next.next.next = new Node(7);
+		head1.next.next.next.next.next.next = head1.next.next.next; // 7->4
+
+		// 0->9->8->2...
+		head2 = new Node(0);
+		head2.next = new Node(9);
+		head2.next.next = new Node(8);
+		head2.next.next.next = head1.next; // 8->2
+		System.out.println(getIntersectNode(head1, head2).value);
+
+		// 0->9->8->6->4->5->6..
+		head2 = new Node(0);
+		head2.next = new Node(9);
+		head2.next.next = new Node(8);
+		head2.next.next.next = head1.next.next.next.next.next; // 8->6
+		System.out.println(getIntersectNode(head1, head2).value);
+
+	}
+
+}
diff --git a/src/class06/Test.java b/src/class06/Test.java
new file mode 100644
index 0000000..831e8d6
--- /dev/null
+++ b/src/class06/Test.java
@@ -0,0 +1,26 @@
+package class06;
+
+public class Test {
+
+	public static class Node{
+		public int value;
+		public Node next;
+		public Node(int v) {
+			value = v;
+		}
+	}
+	
+	public static void main(String[] args) {
+		Node a = new Node(1);
+		Node b = new Node(2);
+		Node c = new Node(3);
+		
+		a.next = b;
+		b.next = c;
+		
+		c = null;
+		
+	}
+	
+	
+}
diff --git a/src/class07/Code01_RecursiveTraversalBT.java b/src/class07/Code01_RecursiveTraversalBT.java
new file mode 100644
index 0000000..56e9bec
--- /dev/null
+++ b/src/class07/Code01_RecursiveTraversalBT.java
@@ -0,0 +1,72 @@
+package class07;
+
+public class Code01_RecursiveTraversalBT {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int v) {
+			value = v;
+		}
+	}
+
+	public static void f(Node head) {
+		if (head == null) {
+			return;
+		}
+		// 1
+		f(head.left);
+		// 2
+		f(head.right);
+		// 3
+	}
+
+	// 先序打印所有节点
+	public static void pre(Node head) {
+		if (head == null) {
+			return;
+		}
+		System.out.println(head.value);
+		pre(head.left);
+		pre(head.right);
+	}
+
+	public static void in(Node head) {
+		if (head == null) {
+			return;
+		}
+		in(head.left);
+		System.out.println(head.value);
+		in(head.right);
+	}
+
+	public static void pos(Node head) {
+		if (head == null) {
+			return;
+		}
+		pos(head.left);
+		pos(head.right);
+		System.out.println(head.value);
+	}
+
+	public static void main(String[] args) {
+		Node head = new Node(1);
+		head.left = new Node(2);
+		head.right = new Node(3);
+		head.left.left = new Node(4);
+		head.left.right = new Node(5);
+		head.right.left = new Node(6);
+		head.right.right = new Node(7);
+
+		pre(head);
+		System.out.println("========");
+		in(head);
+		System.out.println("========");
+		pos(head);
+		System.out.println("========");
+
+	}
+
+}
diff --git a/src/class07/Code02_UnRecursiveTraversalBT.java b/src/class07/Code02_UnRecursiveTraversalBT.java
new file mode 100644
index 0000000..ddff515
--- /dev/null
+++ b/src/class07/Code02_UnRecursiveTraversalBT.java
@@ -0,0 +1,117 @@
+package class07;
+
+import java.util.Stack;
+
+public class Code02_UnRecursiveTraversalBT {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int v) {
+			value = v;
+		}
+	}
+
+	public static void pre(Node head) {
+		System.out.print("pre-order: ");
+		if (head != null) {
+			Stack<Node> stack = new Stack<Node>();
+			stack.add(head);
+			while (!stack.isEmpty()) {
+				head = stack.pop();
+				System.out.print(head.value + " ");
+				if (head.right != null) {
+					stack.push(head.right);
+				}
+				if (head.left != null) {
+					stack.push(head.left);
+				}
+			}
+		}
+		System.out.println();
+	}
+
+	public static void in(Node head) {
+		System.out.print("in-order: ");
+		if (head != null) {
+			Stack<Node> stack = new Stack<Node>();
+			while (!stack.isEmpty() || head != null) {
+				if (head != null) {
+					stack.push(head);
+					head = head.left;
+				} else {
+					head = stack.pop();
+					System.out.print(head.value + " ");
+					head = head.right;
+				}
+			}
+		}
+		System.out.println();
+	}
+
+	public static void pos1(Node head) {
+		System.out.print("pos-order: ");
+		if (head != null) {
+			Stack<Node> s1 = new Stack<Node>();
+			Stack<Node> s2 = new Stack<Node>();
+			s1.push(head);
+			while (!s1.isEmpty()) {
+				head = s1.pop();
+				s2.push(head);
+				if (head.left != null) {
+					s1.push(head.left);
+				}
+				if (head.right != null) {
+					s1.push(head.right);
+				}
+			}
+			while (!s2.isEmpty()) {
+				System.out.print(s2.pop().value + " ");
+			}
+		}
+		System.out.println();
+	}
+
+	public static void pos2(Node h) {
+		System.out.print("pos-order: ");
+		if (h != null) {
+			Stack<Node> stack = new Stack<Node>();
+			stack.push(h);
+			Node c = null;
+			while (!stack.isEmpty()) {
+				c = stack.peek();
+				if (c.left != null && h != c.left && h != c.right) {
+					stack.push(c.left);
+				} else if (c.right != null && h != c.right) {
+					stack.push(c.right);
+				} else {
+					System.out.print(stack.pop().value + " ");
+					h = c;
+				}
+			}
+		}
+		System.out.println();
+	}
+
+	public static void main(String[] args) {
+		Node head = new Node(1);
+		head.left = new Node(2);
+		head.right = new Node(3);
+		head.left.left = new Node(4);
+		head.left.right = new Node(5);
+		head.right.left = new Node(6);
+		head.right.right = new Node(7);
+
+		pre(head);
+		System.out.println("========");
+		in(head);
+		System.out.println("========");
+		pos1(head);
+		System.out.println("========");
+		pos2(head);
+		System.out.println("========");
+	}
+
+}
diff --git a/src/class07/Code03_LevelTraversalBT.java b/src/class07/Code03_LevelTraversalBT.java
new file mode 100644
index 0000000..34bd6b9
--- /dev/null
+++ b/src/class07/Code03_LevelTraversalBT.java
@@ -0,0 +1,49 @@
+package class07;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+public class Code03_LevelTraversalBT {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int v) {
+			value = v;
+		}
+	}
+
+	public static void level(Node head) {
+		if (head == null) {
+			return;
+		}
+		Queue<Node> queue = new LinkedList<>();
+		queue.add(head);
+		while (!queue.isEmpty()) {
+			Node cur = queue.poll();
+			System.out.println(cur.value);
+			if (cur.left != null) {
+				queue.add(cur.left);
+			}
+			if (cur.right != null) {
+				queue.add(cur.right);
+			}
+		}
+	}
+
+	public static void main(String[] args) {
+		Node head = new Node(1);
+		head.left = new Node(2);
+		head.right = new Node(3);
+		head.left.left = new Node(4);
+		head.left.right = new Node(5);
+		head.right.left = new Node(6);
+		head.right.right = new Node(7);
+
+		level(head);
+		System.out.println("========");
+	}
+
+}
diff --git a/src/class07/Code04_SerializeAndReconstructTree.java b/src/class07/Code04_SerializeAndReconstructTree.java
new file mode 100644
index 0000000..7837bd0
--- /dev/null
+++ b/src/class07/Code04_SerializeAndReconstructTree.java
@@ -0,0 +1,159 @@
+package class07;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+public class Code04_SerializeAndReconstructTree {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static Queue<String> preSerial(Node head) {
+		Queue<String> ans = new LinkedList<>();
+		pres(head, ans);
+		return ans;
+	}
+
+	public static void pres(Node head, Queue<String> ans) {
+		if (head == null) {
+			ans.add(null);
+		} else {
+			ans.add(String.valueOf(head.value));
+			pres(head.left, ans);
+			pres(head.right, ans);
+		}
+	}
+
+	public static Node buildByPreQueue(Queue<String> prelist) {
+		if (prelist == null || prelist.size() == 0) {
+			return null;
+		}
+		return preb(prelist);
+	}
+
+	public static Node preb(Queue<String> prelist) {
+		String value = prelist.poll();
+		if (value == null) {
+			return null;
+		}
+		Node head = new Node(Integer.valueOf(value));
+		head.left = preb(prelist);
+		head.right = preb(prelist);
+		return head;
+	}
+
+	public static Queue<String> levelSerial(Node head) {
+		Queue<String> ans = new LinkedList<>();
+		if (head == null) {
+			ans.add(null);
+		} else {
+			ans.add(String.valueOf(head.value));
+			Queue<Node> queue = new LinkedList<Node>();
+			queue.add(head);
+			while (!queue.isEmpty()) {
+				head = queue.poll();
+				if (head.left != null) {
+					ans.add(String.valueOf(head.left.value));
+					queue.add(head.left);
+				} else {
+					ans.add(null);
+				}
+				if (head.right != null) {
+					ans.add(String.valueOf(head.right.value));
+					queue.add(head.right);
+				} else {
+					ans.add(null);
+				}
+			}
+		}
+		return ans;
+	}
+
+	public static Node buildByLevelQueue(Queue<String> levelList) {
+		if (levelList == null || levelList.size() == 0) {
+			return null;
+		}
+		Node head = generateNode(levelList.poll());
+		Queue<Node> queue = new LinkedList<Node>();
+		if (head != null) {
+			queue.add(head);
+		}
+		Node node = null;
+		while (!queue.isEmpty()) {
+			node = queue.poll();
+			node.left = generateNode(levelList.poll());
+			node.right = generateNode(levelList.poll());
+			if (node.left != null) {
+				queue.add(node.left);
+			}
+			if (node.right != null) {
+				queue.add(node.right);
+			}
+		}
+		return head;
+	}
+
+	public static Node generateNode(String val) {
+		if (val == null) {
+			return null;
+		}
+		return new Node(Integer.valueOf(val));
+	}
+
+	// for test
+	public static Node generateRandomBST(int maxLevel, int maxValue) {
+		return generate(1, maxLevel, maxValue);
+	}
+
+	// for test
+	public static Node generate(int level, int maxLevel, int maxValue) {
+		if (level > maxLevel || Math.random() < 0.5) {
+			return null;
+		}
+		Node head = new Node((int) (Math.random() * maxValue));
+		head.left = generate(level + 1, maxLevel, maxValue);
+		head.right = generate(level + 1, maxLevel, maxValue);
+		return head;
+	}
+
+	// for test
+	public static boolean isSameValueStructure(Node head1, Node head2) {
+		if (head1 == null && head2 != null) {
+			return false;
+		}
+		if (head1 != null && head2 == null) {
+			return false;
+		}
+		if (head1 == null && head2 == null) {
+			return true;
+		}
+		if (head1.value != head2.value) {
+			return false;
+		}
+		return isSameValueStructure(head1.left, head2.left) && isSameValueStructure(head1.right, head2.right);
+	}
+
+	public static void main(String[] args) {
+		int maxLevel = 5;
+		int maxValue = 100;
+		int testTimes = 1000000;
+		for (int i = 0; i < testTimes; i++) {
+			Node head = generateRandomBST(maxLevel, maxValue);
+			Queue<String> pre = preSerial(head);
+			Queue<String> level = levelSerial(head);
+			Node preBuild = buildByPreQueue(pre);
+			Node levelBuild = buildByLevelQueue(level);
+			if (!isSameValueStructure(preBuild, levelBuild)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+}
diff --git a/src/class07/Code05_PrintBinaryTree.java b/src/class07/Code05_PrintBinaryTree.java
new file mode 100644
index 0000000..57adbca
--- /dev/null
+++ b/src/class07/Code05_PrintBinaryTree.java
@@ -0,0 +1,74 @@
+package class07;
+
+public class Code05_PrintBinaryTree {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static void printTree(Node head) {
+		System.out.println("Binary Tree:");
+		printInOrder(head, 0, "H", 17);
+		System.out.println();
+	}
+
+	public static void printInOrder(Node head, int height, String to, int len) {
+		if (head == null) {
+			return;
+		}
+		printInOrder(head.right, height + 1, "v", len);
+		String val = to + head.value + to;
+		int lenM = val.length();
+		int lenL = (len - lenM) / 2;
+		int lenR = len - lenM - lenL;
+		val = getSpace(lenL) + val + getSpace(lenR);
+		System.out.println(getSpace(height * len) + val);
+		printInOrder(head.left, height + 1, "^", len);
+	}
+
+	public static String getSpace(int num) {
+		String space = " ";
+		StringBuffer buf = new StringBuffer("");
+		for (int i = 0; i < num; i++) {
+			buf.append(space);
+		}
+		return buf.toString();
+	}
+
+	public static void main(String[] args) {
+		Node head = new Node(1);
+		head.left = new Node(-222222222);
+		head.right = new Node(3);
+		head.left.left = new Node(Integer.MIN_VALUE);
+		head.right.left = new Node(55555555);
+		head.right.right = new Node(66);
+		head.left.left.right = new Node(777);
+		printTree(head);
+
+		head = new Node(1);
+		head.left = new Node(2);
+		head.right = new Node(3);
+		head.left.left = new Node(4);
+		head.right.left = new Node(5);
+		head.right.right = new Node(6);
+		head.left.left.right = new Node(7);
+		printTree(head);
+
+		head = new Node(1);
+		head.left = new Node(1);
+		head.right = new Node(1);
+		head.left.left = new Node(1);
+		head.right.left = new Node(1);
+		head.right.right = new Node(1);
+		head.left.left.right = new Node(1);
+		printTree(head);
+
+	}
+
+}
diff --git a/src/class07/Code06_TreeMaxWidth.java b/src/class07/Code06_TreeMaxWidth.java
new file mode 100644
index 0000000..de2c7d6
--- /dev/null
+++ b/src/class07/Code06_TreeMaxWidth.java
@@ -0,0 +1,114 @@
+package class07;
+
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.Queue;
+
+public class Code06_TreeMaxWidth {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static int maxWidthUseMap(Node head) {
+		if (head == null) {
+			return 0;
+		}
+		Queue<Node> queue = new LinkedList<>();
+		queue.add(head);
+		// key 在 哪一层，value
+		HashMap<Node, Integer> levelMap = new HashMap<>();
+		levelMap.put(head, 1);
+		int curLevel = 1; // 当前你正在统计哪一层的宽度
+		int curLevelNodes = 0; // 当前层curLevel层，宽度目前是多少
+		int max = 0;
+		while (!queue.isEmpty()) {
+			Node cur = queue.poll();
+			int curNodeLevel = levelMap.get(cur);
+			if (cur.left != null) {
+				levelMap.put(cur.left, curNodeLevel + 1);
+				queue.add(cur.left);
+			}
+			if (cur.right != null) {
+				levelMap.put(cur.right, curNodeLevel + 1);
+				queue.add(cur.right);
+			}
+			if (curNodeLevel == curLevel) {
+				curLevelNodes++;
+			} else {
+				max = Math.max(max, curLevelNodes);
+				curLevel++;
+				curLevelNodes = 1;
+			}
+		}
+		max = Math.max(max, curLevelNodes);
+		return max;
+	}
+
+	public static int maxWidthNoMap(Node head) {
+		if (head == null) {
+			return 0;
+		}
+		Queue<Node> queue = new LinkedList<>();
+		queue.add(head);
+		Node curEnd = head; // 当前层，最右节点是谁
+		Node nextEnd = null; // 下一层，最右节点是谁
+		int max = 0;
+		int curLevelNodes = 0; // 当前层的节点数
+		while (!queue.isEmpty()) {
+			Node cur = queue.poll();
+			if (cur.left != null) {
+				queue.add(cur.left);
+				nextEnd = cur.left;
+			}
+			if (cur.right != null) {
+				queue.add(cur.right);
+				nextEnd = cur.right;
+			}
+			curLevelNodes++;
+			if (cur == curEnd) {
+				max = Math.max(max, curLevelNodes);
+				curLevelNodes = 0;
+				curEnd = nextEnd;
+			}
+		}
+		return max;
+	}
+
+	// for test
+	public static Node generateRandomBST(int maxLevel, int maxValue) {
+		return generate(1, maxLevel, maxValue);
+	}
+
+	// for test
+	public static Node generate(int level, int maxLevel, int maxValue) {
+		if (level > maxLevel || Math.random() < 0.5) {
+			return null;
+		}
+		Node head = new Node((int) (Math.random() * maxValue));
+		head.left = generate(level + 1, maxLevel, maxValue);
+		head.right = generate(level + 1, maxLevel, maxValue);
+		return head;
+	}
+
+	public static void main(String[] args) {
+		int maxLevel = 10;
+		int maxValue = 100;
+		int testTimes = 1000000;
+		for (int i = 0; i < testTimes; i++) {
+			Node head = generateRandomBST(maxLevel, maxValue);
+			if (maxWidthUseMap(head) != maxWidthNoMap(head)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+
+	}
+
+}
diff --git a/src/class07/Code07_SuccessorNode.java b/src/class07/Code07_SuccessorNode.java
new file mode 100644
index 0000000..ba365e3
--- /dev/null
+++ b/src/class07/Code07_SuccessorNode.java
@@ -0,0 +1,86 @@
+package class07;
+
+public class Code07_SuccessorNode {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+		public Node parent;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static Node getSuccessorNode(Node node) {
+		if (node == null) {
+			return node;
+		}
+		if (node.right != null) {
+			return getLeftMost(node.right);
+		} else { // 无右子树
+			Node parent = node.parent;
+			while (parent != null && parent.right == node) { // 当前节点是其父亲节点右孩子
+				node = parent;
+				parent = node.parent;
+			}
+			return parent;
+		}
+	}
+
+	public static Node getLeftMost(Node node) {
+		if (node == null) {
+			return node;
+		}
+		while (node.left != null) {
+			node = node.left;
+		}
+		return node;
+	}
+
+	public static void main(String[] args) {
+		Node head = new Node(6);
+		head.parent = null;
+		head.left = new Node(3);
+		head.left.parent = head;
+		head.left.left = new Node(1);
+		head.left.left.parent = head.left;
+		head.left.left.right = new Node(2);
+		head.left.left.right.parent = head.left.left;
+		head.left.right = new Node(4);
+		head.left.right.parent = head.left;
+		head.left.right.right = new Node(5);
+		head.left.right.right.parent = head.left.right;
+		head.right = new Node(9);
+		head.right.parent = head;
+		head.right.left = new Node(8);
+		head.right.left.parent = head.right;
+		head.right.left.left = new Node(7);
+		head.right.left.left.parent = head.right.left;
+		head.right.right = new Node(10);
+		head.right.right.parent = head.right;
+
+		Node test = head.left.left;
+		System.out.println(test.value + " next: " + getSuccessorNode(test).value);
+		test = head.left.left.right;
+		System.out.println(test.value + " next: " + getSuccessorNode(test).value);
+		test = head.left;
+		System.out.println(test.value + " next: " + getSuccessorNode(test).value);
+		test = head.left.right;
+		System.out.println(test.value + " next: " + getSuccessorNode(test).value);
+		test = head.left.right.right;
+		System.out.println(test.value + " next: " + getSuccessorNode(test).value);
+		test = head;
+		System.out.println(test.value + " next: " + getSuccessorNode(test).value);
+		test = head.right.left.left;
+		System.out.println(test.value + " next: " + getSuccessorNode(test).value);
+		test = head.right.left;
+		System.out.println(test.value + " next: " + getSuccessorNode(test).value);
+		test = head.right;
+		System.out.println(test.value + " next: " + getSuccessorNode(test).value);
+		test = head.right.right; // 10's next is null
+		System.out.println(test.value + " next: " + getSuccessorNode(test));
+	}
+
+}
diff --git a/src/class07/Code08_PaperFolding.java b/src/class07/Code08_PaperFolding.java
new file mode 100644
index 0000000..230b47d
--- /dev/null
+++ b/src/class07/Code08_PaperFolding.java
@@ -0,0 +1,24 @@
+package class07;
+
+public class Code08_PaperFolding {
+
+	public static void printAllFolds(int N) {
+		printProcess(1, N, true);
+	}
+
+	// 递归过程，来到了某一个节点，
+	// i是节点的层数，N一共的层数，down == true  凹    down == false 凸
+	public static void printProcess(int i, int N, boolean down) {
+		if (i > N) {
+			return;
+		}
+		printProcess(i + 1, N, true);
+		System.out.println(down ? "凹 " : "凸 ");
+		printProcess(i + 1, N, false);
+	}
+
+	public static void main(String[] args) {
+		int N = 3;
+		printAllFolds(N);
+	}
+}
diff --git a/src/class08/Code01_IsBalanced.java b/src/class08/Code01_IsBalanced.java
new file mode 100644
index 0000000..38238c4
--- /dev/null
+++ b/src/class08/Code01_IsBalanced.java
@@ -0,0 +1,92 @@
+package class08;
+
+public class Code01_IsBalanced {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static boolean isBalanced1(Node head) {
+		boolean[] ans = new boolean[1];
+		ans[0] = true;
+		process1(head, ans);
+		return ans[0];
+	}
+
+	public static int process1(Node head, boolean[] ans) {
+		if (!ans[0] || head == null) {
+			return -1;
+		}
+		int leftHeight = process1(head.left, ans);
+		int rightHeight = process1(head.right, ans);
+		if (Math.abs(leftHeight - rightHeight) > 1) {
+			ans[0] = false;
+		}
+		return Math.max(leftHeight, rightHeight) + 1;
+	}
+
+	public static boolean isBalanced2(Node head) {
+		return process2(head).isBalaced;
+	}
+
+	// 左、右要求一样，Info 信息返回的结构体
+	public static class Info {
+		public boolean isBalaced;
+		public int height;
+
+		public Info(boolean b, int h) {
+			isBalaced = b;
+			height = h;
+		}
+	}
+
+	public static Info process2(Node X) {
+		if (X == null) {
+			return new Info(true, 0);
+		}
+		Info leftInfo = process2(X.left);
+		Info rightInfo = process2(X.right);
+		int height = Math.max(leftInfo.height, rightInfo.height) + 1;
+		boolean isBalanced = true;
+		if (!leftInfo.isBalaced || !rightInfo.isBalaced || Math.abs(leftInfo.height - rightInfo.height) > 1) {
+			isBalanced = false;
+		}
+		return new Info(isBalanced, height);
+	}
+
+	// for test
+	public static Node generateRandomBST(int maxLevel, int maxValue) {
+		return generate(1, maxLevel, maxValue);
+	}
+
+	// for test
+	public static Node generate(int level, int maxLevel, int maxValue) {
+		if (level > maxLevel || Math.random() < 0.5) {
+			return null;
+		}
+		Node head = new Node((int) (Math.random() * maxValue));
+		head.left = generate(level + 1, maxLevel, maxValue);
+		head.right = generate(level + 1, maxLevel, maxValue);
+		return head;
+	}
+
+	public static void main(String[] args) {
+		int maxLevel = 5;
+		int maxValue = 100;
+		int testTimes = 1000000;
+		for (int i = 0; i < testTimes; i++) {
+			Node head = generateRandomBST(maxLevel, maxValue);
+			if (isBalanced1(head) != isBalanced2(head)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class08/Code02_IsFull.java b/src/class08/Code02_IsFull.java
new file mode 100644
index 0000000..1512def
--- /dev/null
+++ b/src/class08/Code02_IsFull.java
@@ -0,0 +1,96 @@
+package class08;
+
+public class Code02_IsFull {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static boolean isFull1(Node head) {
+		if (head == null) {
+			return true;
+		}
+		int height = h(head);
+		int nodes = n(head);
+		return (1 << height) - 1 == nodes;
+	}
+
+	public static int h(Node head) {
+		if (head == null) {
+			return 0;
+		}
+		return Math.max(h(head.left), h(head.right)) + 1;
+	}
+
+	public static int n(Node head) {
+		if (head == null) {
+			return 0;
+		}
+		return n(head.left) + n(head.right) + 1;
+	}
+
+	public static boolean isFull2(Node head) {
+		if (head == null) {
+			return true;
+		}
+		Info all = process(head);
+		return (1 << all.height) - 1 == all.nodes;
+	}
+
+	public static class Info {
+		public int height;
+		public int nodes;
+
+		public Info(int h, int n) {
+			height = h;
+			nodes = n;
+		}
+	}
+
+	public static Info process(Node head) {
+		if (head == null) {
+			return new Info(0, 0);
+		}
+		Info leftInfo = process(head.left);
+		Info rightInfo = process(head.right);
+		int height = Math.max(leftInfo.height, rightInfo.height) + 1;
+		int nodes = leftInfo.nodes + rightInfo.nodes + 1;
+		return new Info(height, nodes);
+	}
+
+	// for test
+	public static Node generateRandomBST(int maxLevel, int maxValue) {
+		return generate(1, maxLevel, maxValue);
+	}
+
+	// for test
+	public static Node generate(int level, int maxLevel, int maxValue) {
+		if (level > maxLevel || Math.random() < 0.5) {
+			return null;
+		}
+		Node head = new Node((int) (Math.random() * maxValue));
+		head.left = generate(level + 1, maxLevel, maxValue);
+		head.right = generate(level + 1, maxLevel, maxValue);
+		return head;
+	}
+
+	public static void main(String[] args) {
+		int maxLevel = 5;
+		int maxValue = 100;
+		int testTimes = 1000000;
+		for (int i = 0; i < testTimes; i++) {
+			Node head = generateRandomBST(maxLevel, maxValue);
+			if (isFull1(head) != isFull2(head)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class08/Code03_IsBST.java b/src/class08/Code03_IsBST.java
new file mode 100644
index 0000000..a6a7922
--- /dev/null
+++ b/src/class08/Code03_IsBST.java
@@ -0,0 +1,115 @@
+package class08;
+
+import java.util.ArrayList;
+
+public class Code03_IsBST {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static boolean isBST1(Node head) {
+		if (head == null) {
+			return true;
+		}
+		ArrayList<Node> arr = new ArrayList<>();
+		in(head, arr);
+		for (int i = 1; i < arr.size(); i++) {
+			if (arr.get(i).value <= arr.get(i - 1).value) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	public static void in(Node head, ArrayList<Node> arr) {
+		if (head == null) {
+			return;
+		}
+		in(head.left, arr);
+		arr.add(head);
+		in(head.right, arr);
+	}
+
+	public static boolean isBST2(Node head) {
+		if (head == null) {
+			return true;
+		}
+		return process(head).isBST;
+	}
+
+	public static class Info {
+		boolean isBST;
+		public int min;
+		public int max;
+
+		public Info(boolean is, int mi, int ma) {
+			isBST = is;
+			min = mi;
+			max = ma;
+		}
+	}
+
+	public static Info process(Node head) {
+		if (head == null) {
+			return null;
+		}
+		Info leftInfo = process(head.left);
+		Info rightInfo = process(head.right);
+		int min = head.value;
+		int max = head.value;
+		if (leftInfo != null) {
+			min = Math.min(min, leftInfo.min);
+			max = Math.max(max, leftInfo.max);
+		}
+		if (rightInfo != null) {
+			min = Math.min(min, rightInfo.min);
+			max = Math.max(max, rightInfo.max);
+		}
+		boolean isBST = false;
+		if (
+			(leftInfo == null ? true : (leftInfo.isBST && leftInfo.max < head.value))
+			&&
+		    (rightInfo == null ? true : (rightInfo.isBST && rightInfo.min > head.value))
+		    		) {
+			isBST = true;
+		}
+		return new Info(isBST, min, max);
+	}
+
+	// for test
+	public static Node generateRandomBST(int maxLevel, int maxValue) {
+		return generate(1, maxLevel, maxValue);
+	}
+
+	// for test
+	public static Node generate(int level, int maxLevel, int maxValue) {
+		if (level > maxLevel || Math.random() < 0.5) {
+			return null;
+		}
+		Node head = new Node((int) (Math.random() * maxValue));
+		head.left = generate(level + 1, maxLevel, maxValue);
+		head.right = generate(level + 1, maxLevel, maxValue);
+		return head;
+	}
+
+	public static void main(String[] args) {
+		int maxLevel = 4;
+		int maxValue = 100;
+		int testTimes = 1000000;
+		for (int i = 0; i < testTimes; i++) {
+			Node head = generateRandomBST(maxLevel, maxValue);
+			if (isBST1(head) != isBST2(head)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class08/Code04_MaxSubBSTSize.java b/src/class08/Code04_MaxSubBSTSize.java
new file mode 100644
index 0000000..2f4116c
--- /dev/null
+++ b/src/class08/Code04_MaxSubBSTSize.java
@@ -0,0 +1,229 @@
+package class08;
+
+import java.util.ArrayList;
+
+public class Code04_MaxSubBSTSize {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static int getBSTSize(Node head) {
+		if (head == null) {
+			return 0;
+		}
+		ArrayList<Node> arr = new ArrayList<>();
+		in(head, arr);
+		for (int i = 1; i < arr.size(); i++) {
+			if (arr.get(i).value <= arr.get(i - 1).value) {
+				return 0;
+			}
+		}
+		return arr.size();
+	}
+
+	public static void in(Node head, ArrayList<Node> arr) {
+		if (head == null) {
+			return;
+		}
+		in(head.left, arr);
+		arr.add(head);
+		in(head.right, arr);
+	}
+
+	public static int maxSubBSTSize1(Node head) {
+		if (head == null) {
+			return 0;
+		}
+		int h = getBSTSize(head);
+		if (h != 0) {
+			return h;
+		}
+		return Math.max(maxSubBSTSize1(head.left), maxSubBSTSize1(head.right));
+	}
+
+	public static int maxSubBSTSize2(Node head) {
+		if (head == null) {
+			return 0;
+		}
+		return process(head).maxSubBSTSize;
+	}
+
+
+
+//	public static Info process(Node head) {
+//		if (head == null) {
+//			return null;
+//		}
+//		Info leftInfo = process(head.left);
+//		Info rightInfo = process(head.right);
+//		int min = head.value;
+//		int max = head.value;
+//		int maxSubBSTSize = 0;
+//		if (leftInfo != null) {
+//			min = Math.min(min, leftInfo.min);
+//			max = Math.max(max, leftInfo.max);
+//			maxSubBSTSize = Math.max(maxSubBSTSize, leftInfo.maxSubBSTSize);
+//		}
+//		if (rightInfo != null) {
+//			min = Math.min(min, rightInfo.min);
+//			max = Math.max(max, rightInfo.max);
+//			maxSubBSTSize = Math.max(maxSubBSTSize, rightInfo.maxSubBSTSize);
+//		}
+//		boolean isBST = false;
+//		if ((leftInfo == null ? true : (leftInfo.isAllBST && leftInfo.max < head.value))
+//				&& (rightInfo == null ? true : (rightInfo.isAllBST && rightInfo.min > head.value))) {
+//			isBST = true;
+//			maxSubBSTSize = (leftInfo == null ? 0 : leftInfo.maxSubBSTSize)
+//					+ (rightInfo == null ? 0 : rightInfo.maxSubBSTSize) + 1;
+//		}
+//		return new Info(isBST, maxSubBSTSize, min, max);
+//	}
+	
+	
+	
+	
+	
+	
+	
+	
+	
+	// 任何子树
+	public static class Info {
+		public boolean isAllBST;
+		public int maxSubBSTSize;
+		public int min;
+		public int max;
+
+		public Info(boolean is, int size, int mi, int ma) {
+			isAllBST = is;
+			maxSubBSTSize = size;
+			min = mi;
+			max = ma;
+		}
+	}
+	
+	
+	
+	
+	public static Info process(Node X) {
+		if(X == null) {
+			return null;
+		}
+		Info leftInfo = process(X.left);
+		Info rightInfo = process(X.right);
+		
+		
+		
+		int min = X.value;
+		int max = X.value;
+		
+		if(leftInfo != null) {
+			min = Math.min(min, leftInfo.min);
+			max = Math.max(max, leftInfo.max);
+		}
+		if(rightInfo != null) {
+			min = Math.min(min, rightInfo.min);
+			max = Math.max(max, rightInfo.max);
+		}
+		
+		
+		
+		
+		
+		
+
+		int maxSubBSTSize = 0;
+		if(leftInfo != null) {
+			maxSubBSTSize = leftInfo.maxSubBSTSize;
+		}
+		if(rightInfo !=null) {
+			maxSubBSTSize = Math.max(maxSubBSTSize, rightInfo.maxSubBSTSize);
+		}
+		boolean isAllBST = false;
+		
+		
+		if(
+				// 左树整体需要是搜索二叉树
+				(  leftInfo == null ? true : leftInfo.isAllBST    )
+				&&
+				(  rightInfo == null ? true : rightInfo.isAllBST    )
+				&&
+				// 左树最大值<x
+				(leftInfo == null ? true : leftInfo.max < X.value)
+				&&
+				(rightInfo == null ? true : rightInfo.min > X.value)
+				
+				
+				) {
+			
+			maxSubBSTSize = 
+					(leftInfo == null ? 0 : leftInfo.maxSubBSTSize)
+					+
+					(rightInfo == null ? 0 : rightInfo.maxSubBSTSize)
+					+
+					1;
+					isAllBST = true;
+			
+			
+		}
+
+		
+		
+		
+		
+		
+		
+		
+		
+		
+		
+		
+		
+		
+		
+		
+		
+		return new Info(isAllBST, maxSubBSTSize, min, max);
+	}
+	
+	
+	
+	
+
+	// for test
+	public static Node generateRandomBST(int maxLevel, int maxValue) {
+		return generate(1, maxLevel, maxValue);
+	}
+
+	// for test
+	public static Node generate(int level, int maxLevel, int maxValue) {
+		if (level > maxLevel || Math.random() < 0.5) {
+			return null;
+		}
+		Node head = new Node((int) (Math.random() * maxValue));
+		head.left = generate(level + 1, maxLevel, maxValue);
+		head.right = generate(level + 1, maxLevel, maxValue);
+		return head;
+	}
+
+	public static void main(String[] args) {
+		int maxLevel = 4;
+		int maxValue = 100;
+		int testTimes = 1000000;
+		for (int i = 0; i < testTimes; i++) {
+			Node head = generateRandomBST(maxLevel, maxValue);
+			if (maxSubBSTSize1(head) != maxSubBSTSize2(head)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class08/Code05_MaxSubBSTHead.java b/src/class08/Code05_MaxSubBSTHead.java
new file mode 100644
index 0000000..70c01bb
--- /dev/null
+++ b/src/class08/Code05_MaxSubBSTHead.java
@@ -0,0 +1,135 @@
+package class08;
+
+import java.util.ArrayList;
+
+public class Code05_MaxSubBSTHead {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static int getBSTSize(Node head) {
+		if (head == null) {
+			return 0;
+		}
+		ArrayList<Node> arr = new ArrayList<>();
+		in(head, arr);
+		for (int i = 1; i < arr.size(); i++) {
+			if (arr.get(i).value <= arr.get(i - 1).value) {
+				return 0;
+			}
+		}
+		return arr.size();
+	}
+
+	public static void in(Node head, ArrayList<Node> arr) {
+		if (head == null) {
+			return;
+		}
+		in(head.left, arr);
+		arr.add(head);
+		in(head.right, arr);
+	}
+
+	public static Node maxSubBSTHead1(Node head) {
+		if (head == null) {
+			return null;
+		}
+		if (getBSTSize(head) != 0) {
+			return head;
+		}
+		Node leftAns = maxSubBSTHead1(head.left);
+		Node rightAns = maxSubBSTHead1(head.right);
+		return getBSTSize(leftAns) >= getBSTSize(rightAns) ? leftAns : rightAns;
+	}
+
+	public static Node maxSubBSTHead2(Node head) {
+		if (head == null) {
+			return null;
+		}
+		return process(head).maxSubBSTHead;
+	}
+
+	public static class Info {
+		public Node maxSubBSTHead;
+		public int maxSubBSTSize;
+		public int min;
+		public int max;
+
+		public Info(Node h, int size, int mi, int ma) {
+			maxSubBSTHead = h;
+			maxSubBSTSize = size;
+			min = mi;
+			max = ma;
+		}
+	}
+
+	public static Info process(Node head) {
+		if (head == null) {
+			return null;
+		}
+		Info leftInfo = process(head.left);
+		Info rightInfo = process(head.right);
+		int min = head.value;
+		int max = head.value;
+		Node maxSubBSTHead = null;
+		int maxSubBSTSize = 0;
+		if (leftInfo != null) {
+			min = Math.min(min, leftInfo.min);
+			max = Math.max(max, leftInfo.max);
+			maxSubBSTHead = leftInfo.maxSubBSTHead;
+			maxSubBSTSize = leftInfo.maxSubBSTSize;
+		}
+		if (rightInfo != null) {
+			min = Math.min(min, rightInfo.min);
+			max = Math.max(max, rightInfo.max);
+			if (rightInfo.maxSubBSTSize > maxSubBSTSize) {
+				maxSubBSTHead = rightInfo.maxSubBSTHead;
+				maxSubBSTSize = rightInfo.maxSubBSTSize;
+			}
+		}
+		if ((leftInfo == null ? true : (leftInfo.maxSubBSTHead == head.left && leftInfo.max < head.value))
+				&& (rightInfo == null ? true : (rightInfo.maxSubBSTHead == head.right && rightInfo.min > head.value))) {
+			maxSubBSTHead = head;
+			maxSubBSTSize = (leftInfo == null ? 0 : leftInfo.maxSubBSTSize)
+					+ (rightInfo == null ? 0 : rightInfo.maxSubBSTSize) + 1;
+		}
+		return new Info(maxSubBSTHead, maxSubBSTSize, min, max);
+	}
+
+	// for test
+	public static Node generateRandomBST(int maxLevel, int maxValue) {
+		return generate(1, maxLevel, maxValue);
+	}
+
+	// for test
+	public static Node generate(int level, int maxLevel, int maxValue) {
+		if (level > maxLevel || Math.random() < 0.5) {
+			return null;
+		}
+		Node head = new Node((int) (Math.random() * maxValue));
+		head.left = generate(level + 1, maxLevel, maxValue);
+		head.right = generate(level + 1, maxLevel, maxValue);
+		return head;
+	}
+
+	public static void main(String[] args) {
+		int maxLevel = 4;
+		int maxValue = 100;
+		int testTimes = 1000000;
+		for (int i = 0; i < testTimes; i++) {
+			Node head = generateRandomBST(maxLevel, maxValue);
+			if (maxSubBSTHead1(head) != maxSubBSTHead2(head)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class08/Code06_IsCBT.java b/src/class08/Code06_IsCBT.java
new file mode 100644
index 0000000..6fc3df4
--- /dev/null
+++ b/src/class08/Code06_IsCBT.java
@@ -0,0 +1,124 @@
+package class08;
+
+import java.util.LinkedList;
+
+public class Code06_IsCBT {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static boolean isCBT1(Node head) {
+		if (head == null) {
+			return true;
+		}
+		LinkedList<Node> queue = new LinkedList<>();
+		// 是否遇到过左右两个孩子不双全的节点
+		boolean leaf = false;
+		Node l = null;
+		Node r = null;
+		queue.add(head);
+		while (!queue.isEmpty()) {
+			head = queue.poll();
+			l = head.left;
+			r = head.right;
+			if (
+			// 如果遇到了不双全的节点之后，又发现当前节点不是叶节点
+			(leaf && !(l == null && r == null)) || (l == null && r != null)) {
+				return false;
+			}
+			if (l != null) {
+				queue.add(l);
+			}
+			if (r != null) {
+				queue.add(r);
+			}
+			if (l == null || r == null) {
+				leaf = true;
+			}
+		}
+		return true;
+	}
+
+	public static boolean isCBT2(Node head) {
+		if (head == null) {
+			return true;
+		}
+		return process(head).isCBT;
+	}
+
+	public static class Info {
+		public boolean isFull;
+		public boolean isCBT;
+		public int height;
+
+		public Info(boolean full, boolean cbt, int h) {
+			isFull = full;
+			isCBT = cbt;
+			height = h;
+		}
+	}
+
+	public static Info process(Node head) {
+		if (head == null) {
+			return new Info(true, true, 0);
+		}
+		Info leftInfo = process(head.left);
+		Info rightInfo = process(head.right);
+		int height = Math.max(leftInfo.height, rightInfo.height) + 1;
+		boolean isFull = leftInfo.isFull && rightInfo.isFull && leftInfo.height == rightInfo.height;
+		boolean isCBT = false;
+		if (isFull) {
+			isCBT = true;
+		} else {
+			if (leftInfo.isCBT && rightInfo.isCBT) {
+				if (leftInfo.isCBT && rightInfo.isFull && leftInfo.height == rightInfo.height + 1) {
+					isCBT = true;
+				}
+				if (leftInfo.isFull && rightInfo.isFull && leftInfo.height == rightInfo.height + 1) {
+					isCBT = true;
+				}
+				if (leftInfo.isFull && rightInfo.isCBT && leftInfo.height == rightInfo.height) {
+					isCBT = true;
+				}
+			}
+		}
+		return new Info(isFull, isCBT, height);
+	}
+
+	// for test
+	public static Node generateRandomBST(int maxLevel, int maxValue) {
+		return generate(1, maxLevel, maxValue);
+	}
+
+	// for test
+	public static Node generate(int level, int maxLevel, int maxValue) {
+		if (level > maxLevel || Math.random() < 0.5) {
+			return null;
+		}
+		Node head = new Node((int) (Math.random() * maxValue));
+		head.left = generate(level + 1, maxLevel, maxValue);
+		head.right = generate(level + 1, maxLevel, maxValue);
+		return head;
+	}
+
+	public static void main(String[] args) {
+		int maxLevel = 5;
+		int maxValue = 100;
+		int testTimes = 1000000;
+		for (int i = 0; i < testTimes; i++) {
+			Node head = generateRandomBST(maxLevel, maxValue);
+			if (isCBT1(head) != isCBT2(head)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class08/Code07_lowestAncestor.java b/src/class08/Code07_lowestAncestor.java
new file mode 100644
index 0000000..a97f4be
--- /dev/null
+++ b/src/class08/Code07_lowestAncestor.java
@@ -0,0 +1,143 @@
+package class08;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+
+public class Code07_lowestAncestor {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static Node lowestAncestor1(Node head, Node o1, Node o2) {
+		if (head == null) {
+			return null;
+		}
+		HashMap<Node, Node> parentMap = new HashMap<>();
+		parentMap.put(head, null);
+		fillParentMap(head, parentMap);
+		HashSet<Node> o1Set = new HashSet<>();
+		Node cur = o1;
+		o1Set.add(cur);
+		while (parentMap.get(cur) != null) {
+			cur = parentMap.get(cur);
+			o1Set.add(cur);
+		}
+		cur = o2;
+		while (!o1Set.contains(cur)) {
+			cur = parentMap.get(cur);
+		}
+		return cur;
+	}
+
+	public static void fillParentMap(Node head, HashMap<Node, Node> parentMap) {
+		if (head.left != null) {
+			parentMap.put(head.left, head);
+			fillParentMap(head.left, parentMap);
+		}
+		if (head.right != null) {
+			parentMap.put(head.right, head);
+			fillParentMap(head.right, parentMap);
+		}
+	}
+
+	public static Node lowestAncestor2(Node head, Node o1, Node o2) {
+		return process(head, o1, o2).ans;
+	}
+
+	public static class Info {
+		public Node ans;
+		public boolean findO1;
+		public boolean findO2;
+
+		public Info(Node a, boolean f1, boolean f2) {
+			ans = a;
+			findO1 = f1;
+			findO2 = f2;
+		}
+	}
+
+	public static Info process(Node head, Node o1, Node o2) {
+		if (head == null) {
+			return new Info(null, false, false);
+		}
+		Info leftInfo = process(head.left, o1, o2);
+		Info rightInfo = process(head.right, o1, o2);
+
+		boolean findO1 = head == o1 || leftInfo.findO1 || rightInfo.findO1;
+		boolean findO2 = head == o2 || leftInfo.findO2 || rightInfo.findO2;
+		Node ans = null;
+		if (leftInfo.ans != null) {
+			ans = leftInfo.ans;
+		}
+		if (rightInfo.ans != null) {
+			ans = rightInfo.ans;
+		}
+		if (ans == null) {
+			if (findO1 && findO2) {
+				ans = head;
+			}
+		}
+		return new Info(ans, findO1, findO2);
+	}
+
+	// for test
+	public static Node generateRandomBST(int maxLevel, int maxValue) {
+		return generate(1, maxLevel, maxValue);
+	}
+
+	// for test
+	public static Node generate(int level, int maxLevel, int maxValue) {
+		if (level > maxLevel || Math.random() < 0.5) {
+			return null;
+		}
+		Node head = new Node((int) (Math.random() * maxValue));
+		head.left = generate(level + 1, maxLevel, maxValue);
+		head.right = generate(level + 1, maxLevel, maxValue);
+		return head;
+	}
+
+	// for test
+	public static Node pickRandomOne(Node head) {
+		if (head == null) {
+			return null;
+		}
+		ArrayList<Node> arr = new ArrayList<>();
+		fillPrelist(head, arr);
+		int randomIndex = (int) (Math.random() * arr.size());
+		return arr.get(randomIndex);
+	}
+
+	// for test
+	public static void fillPrelist(Node head, ArrayList<Node> arr) {
+		if (head == null) {
+			return;
+		}
+		arr.add(head);
+		fillPrelist(head.left, arr);
+		fillPrelist(head.right, arr);
+	}
+
+	public static void main(String[] args) {
+		int maxLevel = 4;
+		int maxValue = 100;
+		int testTimes = 1000000;
+		for (int i = 0; i < testTimes; i++) {
+			Node head = generateRandomBST(maxLevel, maxValue);
+			Node o1 = pickRandomOne(head);
+			Node o2 = pickRandomOne(head);
+			if (lowestAncestor1(head, o1, o2) != lowestAncestor2(head, o1, o2)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class08/Code08_MaxDistance.java b/src/class08/Code08_MaxDistance.java
new file mode 100644
index 0000000..1fd6e95
--- /dev/null
+++ b/src/class08/Code08_MaxDistance.java
@@ -0,0 +1,151 @@
+package class08;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+
+public class Code08_MaxDistance {
+
+	public static class Node {
+		public int value;
+		public Node left;
+		public Node right;
+
+		public Node(int data) {
+			this.value = data;
+		}
+	}
+
+	public static int maxDistance1(Node head) {
+		if (head == null) {
+			return 0;
+		}
+		ArrayList<Node> arr = getPrelist(head);
+		HashMap<Node, Node> parentMap = getParentMap(head);
+		int max = 0;
+		for (int i = 0; i < arr.size(); i++) {
+			for (int j = i; j < arr.size(); j++) {
+				max = Math.max(max, distance(parentMap, arr.get(i), arr.get(j)));
+			}
+		}
+		return max;
+	}
+
+	public static ArrayList<Node> getPrelist(Node head) {
+		ArrayList<Node> arr = new ArrayList<>();
+		fillPrelist(head, arr);
+		return arr;
+	}
+
+	public static void fillPrelist(Node head, ArrayList<Node> arr) {
+		if (head == null) {
+			return;
+		}
+		arr.add(head);
+		fillPrelist(head.left, arr);
+		fillPrelist(head.right, arr);
+	}
+
+	public static HashMap<Node, Node> getParentMap(Node head) {
+		HashMap<Node, Node> map = new HashMap<>();
+		map.put(head, null);
+		fillParentMap(head, map);
+		return map;
+	}
+
+	public static void fillParentMap(Node head, HashMap<Node, Node> parentMap) {
+		if (head.left != null) {
+			parentMap.put(head.left, head);
+			fillParentMap(head.left, parentMap);
+		}
+		if (head.right != null) {
+			parentMap.put(head.right, head);
+			fillParentMap(head.right, parentMap);
+		}
+	}
+
+	public static int distance(HashMap<Node, Node> parentMap, Node o1, Node o2) {
+		HashSet<Node> o1Set = new HashSet<>();
+		Node cur = o1;
+		o1Set.add(cur);
+		while (parentMap.get(cur) != null) {
+			cur = parentMap.get(cur);
+			o1Set.add(cur);
+		}
+		cur = o2;
+		while (!o1Set.contains(cur)) {
+			cur = parentMap.get(cur);
+		}
+		Node lowestAncestor = cur;
+		cur = o1;
+		int distance1 = 1;
+		while (cur != lowestAncestor) {
+			cur = parentMap.get(cur);
+			distance1++;
+		}
+		cur = o2;
+		int distance2 = 1;
+		while (cur != lowestAncestor) {
+			cur = parentMap.get(cur);
+			distance2++;
+		}
+		return distance1 + distance2 - 1;
+	}
+
+	public static int maxDistance2(Node head) {
+		return process(head).maxDistance;
+	}
+
+	public static class Info {
+		public int maxDistance;
+		public int height;
+
+		public Info(int dis, int h) {
+			maxDistance = dis;
+			height = h;
+		}
+	}
+
+	public static Info process(Node X) {
+		if (X == null) {
+			return new Info(0, 0);
+		}
+		Info leftInfo = process(X.left);
+		Info rightInfo = process(X.right);
+		int height = Math.max(leftInfo.height, rightInfo.height) + 1;
+		int maxDistance = Math.max(
+				Math.max(leftInfo.maxDistance, rightInfo.maxDistance),
+				leftInfo.height + rightInfo.height + 1);
+		return new Info(maxDistance, height);
+	}
+
+	// for test
+	public static Node generateRandomBST(int maxLevel, int maxValue) {
+		return generate(1, maxLevel, maxValue);
+	}
+
+	// for test
+	public static Node generate(int level, int maxLevel, int maxValue) {
+		if (level > maxLevel || Math.random() < 0.5) {
+			return null;
+		}
+		Node head = new Node((int) (Math.random() * maxValue));
+		head.left = generate(level + 1, maxLevel, maxValue);
+		head.right = generate(level + 1, maxLevel, maxValue);
+		return head;
+	}
+
+	public static void main(String[] args) {
+		int maxLevel = 4;
+		int maxValue = 100;
+		int testTimes = 1000000;
+		for (int i = 0; i < testTimes; i++) {
+			Node head = generateRandomBST(maxLevel, maxValue);
+			if (maxDistance1(head) != maxDistance2(head)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class08/Code09_MaxHappy.java b/src/class08/Code09_MaxHappy.java
new file mode 100644
index 0000000..32294ea
--- /dev/null
+++ b/src/class08/Code09_MaxHappy.java
@@ -0,0 +1,113 @@
+package class08;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Code09_MaxHappy {
+
+	public static class Employee {
+		public int happy;
+		public List<Employee> nexts;
+
+		public Employee(int h) {
+			happy = h;
+			nexts = new ArrayList<>();
+		}
+
+	}
+
+	public static int maxHappy1(Employee boss) {
+		if (boss == null) {
+			return 0;
+		}
+		return process1(boss, false);
+	}
+
+	public static int process1(Employee cur, boolean up) {
+		if (up) {
+			int ans = 0;
+			for (Employee next : cur.nexts) {
+				ans += process1(next, false);
+			}
+			return ans;
+		} else {
+			int p1 = cur.happy;
+			int p2 = 0;
+			for (Employee next : cur.nexts) {
+				p1 += process1(next, true);
+				p2 += process1(next, false);
+			}
+			return Math.max(p1, p2);
+		}
+	}
+
+	public static int maxHappy2(Employee boss) {
+		if (boss == null) {
+			return 0;
+		}
+		Info all = process2(boss);
+		return Math.max(all.yes, all.no);
+	}
+
+	public static class Info {
+		public int yes;
+		public int no;
+
+		public Info(int y, int n) {
+			yes = y;
+			no = n;
+		}
+	}
+
+	public static Info process2(Employee x) {
+		if (x.nexts.isEmpty()) {
+			return new Info(x.happy, 0);
+		}
+		int yes = x.happy;
+		int no = 0;
+		for (Employee next : x.nexts) {
+			Info nextInfo = process2(next);
+			yes += nextInfo.no;
+			no += Math.max(nextInfo.yes, nextInfo.no);
+		}
+		return new Info(yes, no);
+	}
+
+	// for test
+	public static Employee genarateBoss(int maxLevel, int maxNexts, int maxHappy) {
+		if (Math.random() < 0.02) {
+			return null;
+		}
+		Employee boss = new Employee((int) (Math.random() * (maxHappy + 1)));
+		genarateNexts(boss, 1, maxLevel, maxNexts, maxHappy);
+		return boss;
+	}
+
+	// for test
+	public static void genarateNexts(Employee e, int level, int maxLevel, int maxNexts, int maxHappy) {
+		if (level > maxLevel) {
+			return;
+		}
+		int nextsSize = (int) (Math.random() * (maxNexts + 1));
+		for (int i = 0; i < nextsSize; i++) {
+			Employee next = new Employee((int) (Math.random() * (maxHappy + 1)));
+			e.nexts.add(next);
+			genarateNexts(next, level + 1, maxLevel, maxNexts, maxHappy);
+		}
+	}
+
+	public static void main(String[] args) {
+		int maxLevel = 4;
+		int maxNexts = 7;
+		int maxHappy = 100;
+		int testTimes = 100000;
+		for (int i = 0; i < testTimes; i++) {
+			Employee boss = genarateBoss(maxLevel, maxNexts, maxHappy);
+			if (maxHappy1(boss) != maxHappy2(boss)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class09/Code01_LowestLexicography.java b/src/class09/Code01_LowestLexicography.java
new file mode 100644
index 0000000..d3f7b57
--- /dev/null
+++ b/src/class09/Code01_LowestLexicography.java
@@ -0,0 +1,101 @@
+package class09;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.HashSet;
+
+public class Code01_LowestLexicography {
+
+	public static String lowestString1(String[] strs) {
+		if (strs == null || strs.length == 0) {
+			return "";
+		}
+		ArrayList<String> all = new ArrayList<>();
+		HashSet<Integer> use = new HashSet<>();
+		process(strs, use, "", all);
+		String lowest = all.get(0);
+		for (int i = 1; i < all.size(); i++) {
+			if (all.get(i).compareTo(lowest) < 0) {
+				lowest = all.get(i);
+			}
+		}
+		return lowest;
+	}
+
+	public static void process(String[] strs, HashSet<Integer> use, String path, ArrayList<String> all) {
+		if (use.size() == strs.length) {
+			all.add(path);
+		} else {
+			for (int i = 0; i < strs.length; i++) {
+				if (!use.contains(i)) {
+					use.add(i);
+					process(strs, use, path + strs[i], all);
+					use.remove(i);
+				}
+			}
+		}
+	}
+
+	public static class MyComparator implements Comparator<String> {
+		@Override
+		public int compare(String a, String b) {
+			return (a + b).compareTo(b + a);
+		}
+	}
+
+	public static String lowestString2(String[] strs) {
+		if (strs == null || strs.length == 0) {
+			return "";
+		}
+		Arrays.sort(strs, new MyComparator());
+		String res = "";
+		for (int i = 0; i < strs.length; i++) {
+			res += strs[i];
+		}
+		return res;
+	}
+
+	// for test
+	public static String generateRandomString(int strLen) {
+		char[] ans = new char[(int) (Math.random() * strLen) + 1];
+		for (int i = 0; i < ans.length; i++) {
+			int value = (int) (Math.random() * 5);
+			ans[i] = (char) (97 + value);
+		}
+		return String.valueOf(ans);
+	}
+
+	// for test
+	public static String[] generateRandomStringArray(int arrLen, int strLen) {
+		String[] ans = new String[(int) (Math.random() * arrLen) + 1];
+		for (int i = 0; i < ans.length; i++) {
+			ans[i] = generateRandomString(strLen);
+		}
+		return ans;
+	}
+
+	// for test
+	public static String[] copyStringArray(String[] arr) {
+		String[] ans = new String[arr.length];
+		for (int i = 0; i < ans.length; i++) {
+			ans[i] = String.valueOf(arr[i]);
+		}
+		return ans;
+	}
+
+	public static void main(String[] args) {
+		int arrLen = 6;
+		int strLen = 5;
+		int testTimes = 100000;
+		for (int i = 0; i < testTimes; i++) {
+			String[] arr1 = generateRandomStringArray(arrLen, strLen);
+			String[] arr2 = copyStringArray(arr1);
+			if (!lowestString1(arr1).equals(lowestString2(arr2))) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class09/Code02_Light.java b/src/class09/Code02_Light.java
new file mode 100644
index 0000000..b892240
--- /dev/null
+++ b/src/class09/Code02_Light.java
@@ -0,0 +1,81 @@
+package class09;
+
+import java.util.HashSet;
+
+public class Code02_Light {
+
+	public static int minLight1(String road) {
+		if (road == null || road.length() == 0) {
+			return 0;
+		}
+		return process(road.toCharArray(), 0, new HashSet<>());
+	}
+
+	public static int process(char[] str, int index, HashSet<Integer> lights) {
+		if (index == str.length) {
+			for (int i = 0; i < str.length; i++) {
+				if (str[i] != 'X') {
+					if (!lights.contains(i - 1) && !lights.contains(i) && !lights.contains(i + 1)) {
+						return Integer.MAX_VALUE;
+					}
+				}
+			}
+			return lights.size();
+		} else {
+			int no = process(str, index + 1, lights);
+			int yes = Integer.MAX_VALUE;
+			if (str[index] == '.') {
+				lights.add(index);
+				yes = process(str, index + 1, lights);
+				lights.remove(index);
+			}
+			return Math.min(no, yes);
+		}
+	}
+
+	public static int minLight2(String road) {
+		char[] str = road.toCharArray();
+		int index = 0;
+		int light = 0;
+		while (index < str.length) {
+			if (str[index] == 'X') {
+				index++;
+			} else {
+				light++;
+				if (index + 1 == str.length) {
+					break;
+				} else {
+					if (str[index + 1] == 'X') {
+						index = index + 2;
+					} else {
+						index = index + 3;
+					}
+				}
+			}
+		}
+		return light;
+	}
+
+	// for test
+	public static String randomString(int len) {
+		char[] res = new char[(int) (Math.random() * len) + 1];
+		for (int i = 0; i < res.length; i++) {
+			res[i] = Math.random() < 0.5 ? 'X' : '.';
+		}
+		return String.valueOf(res);
+	}
+
+	public static void main(String[] args) {
+		int len = 20;
+		int testTime = 100000;
+		for (int i = 0; i < testTime; i++) {
+			String test = randomString(len);
+			int ans1 = minLight1(test);
+			int ans2 = minLight2(test);
+			if (ans1 != ans2) {
+				System.out.println("oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+}
diff --git a/src/class09/Code03_LessMoneySplitGold.java b/src/class09/Code03_LessMoneySplitGold.java
new file mode 100644
index 0000000..3838941
--- /dev/null
+++ b/src/class09/Code03_LessMoneySplitGold.java
@@ -0,0 +1,76 @@
+package class09;
+
+import java.util.PriorityQueue;
+
+public class Code03_LessMoneySplitGold {
+
+	public static int lessMoney1(int[] arr) {
+		if (arr == null || arr.length == 0) {
+			return 0;
+		}
+		return process(arr, 0);
+	}
+
+	public static int process(int[] arr, int pre) {
+		if (arr.length == 1) {
+			return pre;
+		}
+		int ans = Integer.MAX_VALUE;
+		for (int i = 0; i < arr.length; i++) {
+			for (int j = i + 1; j < arr.length; j++) {
+				ans = Math.min(ans, process(copyAndMergeTwo(arr, i, j), pre + arr[i] + arr[j]));
+			}
+		}
+		return ans;
+	}
+
+	public static int[] copyAndMergeTwo(int[] arr, int i, int j) {
+		int[] ans = new int[arr.length - 1];
+		int ansi = 0;
+		for (int arri = 0; arri < arr.length; arri++) {
+			if (arri != i && arri != j) {
+				ans[ansi++] = arr[arri];
+			}
+		}
+		ans[ansi] = arr[i] + arr[j];
+		return ans;
+	}
+
+	public static int lessMoney2(int[] arr) {
+		PriorityQueue<Integer> pQ = new PriorityQueue<>();
+		for (int i = 0; i < arr.length; i++) {
+			pQ.add(arr[i]);
+		}
+		int sum = 0;
+		int cur = 0;
+		while (pQ.size() > 1) {
+			cur = pQ.poll() + pQ.poll();
+			sum += cur;
+			pQ.add(cur);
+		}
+		return sum;
+	}
+
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) (Math.random() * (maxValue + 1));
+		}
+		return arr;
+	}
+
+	public static void main(String[] args) {
+		int testTime = 100000;
+		int maxSize = 6;
+		int maxValue = 1000;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr = generateRandomArray(maxSize, maxValue);
+			if (lessMoney1(arr) != lessMoney2(arr)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class09/Code04_BestArrange.java b/src/class09/Code04_BestArrange.java
new file mode 100644
index 0000000..2b5711a
--- /dev/null
+++ b/src/class09/Code04_BestArrange.java
@@ -0,0 +1,100 @@
+package class09;
+
+import java.util.Arrays;
+import java.util.Comparator;
+
+public class Code04_BestArrange {
+
+	public static class Program {
+		public int start;
+		public int end;
+
+		public Program(int start, int end) {
+			this.start = start;
+			this.end = end;
+		}
+	}
+
+	public static int bestArrange1(Program[] programs) {
+		if (programs == null || programs.length == 0) {
+			return 0;
+		}
+		return process(programs, 0, 0);
+	}
+
+	public static int process(Program[] programs, int done, int timeLine) {
+		if (programs.length == 0) {
+			return done;
+		}
+		int max = done;
+		for (int i = 0; i < programs.length; i++) {
+			if (programs[i].start >= timeLine) {
+				Program[] next = copyButExcept(programs, i);
+				max = Math.max(max, process(next, done + 1, programs[i].end));
+			}
+		}
+		return max;
+	}
+
+	public static Program[] copyButExcept(Program[] programs, int i) {
+		Program[] ans = new Program[programs.length - 1];
+		int index = 0;
+		for (int k = 0; k < programs.length; k++) {
+			if (k != i) {
+				ans[index++] = programs[k];
+			}
+		}
+		return ans;
+	}
+
+	public static int bestArrange2(Program[] programs) {
+		Arrays.sort(programs, new ProgramComparator());
+		int timeLine = 0;
+		int result = 0;
+		for (int i = 0; i < programs.length; i++) {
+			if (timeLine <= programs[i].start) {
+				result++;
+				timeLine = programs[i].end;
+			}
+		}
+		return result;
+	}
+
+	public static class ProgramComparator implements Comparator<Program> {
+
+		@Override
+		public int compare(Program o1, Program o2) {
+			return o1.end - o2.end;
+		}
+
+	}
+
+	// for test
+	public static Program[] generatePrograms(int programSize, int timeMax) {
+		Program[] ans = new Program[(int) (Math.random() * (programSize + 1))];
+		for (int i = 0; i < ans.length; i++) {
+			int r1 = (int) (Math.random() * (timeMax + 1));
+			int r2 = (int) (Math.random() * (timeMax + 1));
+			if (r1 == r2) {
+				ans[i] = new Program(r1, r1 + 1);
+			} else {
+				ans[i] = new Program(Math.min(r1, r2), Math.max(r1, r2));
+			}
+		}
+		return ans;
+	}
+
+	public static void main(String[] args) {
+		int programSize = 12;
+		int timeMax = 20;
+		int timeTimes = 1000000;
+		for (int i = 0; i < timeTimes; i++) {
+			Program[] programs = generatePrograms(programSize, timeMax);
+			if (bestArrange1(programs) != bestArrange2(programs)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/src/class09/Code05_IPO.java b/src/class09/Code05_IPO.java
new file mode 100644
index 0000000..bde9d89
--- /dev/null
+++ b/src/class09/Code05_IPO.java
@@ -0,0 +1,54 @@
+package class09;
+
+import java.util.Comparator;
+import java.util.PriorityQueue;
+
+public class Code05_IPO {
+
+	public static int findMaximizedCapital(int K, int W, int[] Profits, int[] Capital) {
+		PriorityQueue<Program> minCostQ = new PriorityQueue<>(new MinCostComparator());
+		PriorityQueue<Program> maxProfitQ = new PriorityQueue<>(new MaxProfitComparator());
+		for (int i = 0; i < Profits.length; i++) {
+			minCostQ.add(new Program(Profits[i], Capital[i]));
+		}
+		for (int i = 0; i < K; i++) {
+			while (!minCostQ.isEmpty() && minCostQ.peek().c <= W) {
+				maxProfitQ.add(minCostQ.poll());
+			}
+			if (maxProfitQ.isEmpty()) {
+				return W;
+			}
+			W += maxProfitQ.poll().p;
+		}
+		return W;
+	}
+
+	public static class Program {
+		public int p;
+		public int c;
+
+		public Program(int p, int c) {
+			this.p = p;
+			this.c = c;
+		}
+	}
+
+	public static class MinCostComparator implements Comparator<Program> {
+
+		@Override
+		public int compare(Program o1, Program o2) {
+			return o1.c - o2.c;
+		}
+
+	}
+
+	public static class MaxProfitComparator implements Comparator<Program> {
+
+		@Override
+		public int compare(Program o1, Program o2) {
+			return o2.p - o1.p;
+		}
+
+	}
+
+}
diff --git a/src/class10/Code01_UnionFind.java b/src/class10/Code01_UnionFind.java
new file mode 100644
index 0000000..3421427
--- /dev/null
+++ b/src/class10/Code01_UnionFind.java
@@ -0,0 +1,73 @@
+package class10;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Stack;
+
+public class Code01_UnionFind {
+
+	public static class Node<V> {
+		V value;
+
+		public Node(V v) {
+			value = v;
+		}
+	}
+
+	public static class UnionSet<V> {
+		public HashMap<V, Node<V>> nodes;
+		public HashMap<Node<V>, Node<V>> parents;
+		public HashMap<Node<V>, Integer> sizeMap;
+
+		public UnionSet(List<V> values) {
+			for (V value : values) {
+				Node<V> node = new Node<>(value);
+				nodes.put(value, node);
+				parents.put(node, node);
+				sizeMap.put(node, 1);
+			}
+		}
+
+		public Node<V> findFather(Node<V> cur) {
+			Stack<Node<V>> path = new Stack<>();
+			while (cur != parents.get(cur)) {
+				path.push(cur);
+				cur = parents.get(cur);
+			}
+			// cur头节点
+			while (!path.isEmpty()) {
+				parents.put(path.pop(), cur);
+			}
+			return cur;
+		}
+
+		public boolean isSameSet(V a, V b) {
+			if (!nodes.containsKey(a) || !nodes.containsKey(b)) {
+				return false;
+			}
+			return findFather(nodes.get(a)) == findFather(nodes.get(b));
+		}
+
+		public void union(V a, V b) {
+			if (!nodes.containsKey(a) || !nodes.containsKey(b)) {
+				return;
+			}
+			Node<V> aHead = findFather(nodes.get(a));
+			Node<V> bHead = findFather(nodes.get(b));
+			if (aHead != bHead) {
+				int aSetSize = sizeMap.get(aHead);
+				int bSetSize = sizeMap.get(bHead);
+				if (aSetSize >= bSetSize) {
+					parents.put(bHead, aHead);
+					sizeMap.put(aHead, aSetSize + bSetSize);
+					sizeMap.remove(bHead);
+				} else {
+					parents.put(aHead, bHead);
+					sizeMap.put(bHead, aSetSize + bSetSize);
+					sizeMap.remove(aHead);
+				}
+			}
+		}
+	}
+
+}
diff --git a/src/class10/Code02_BFS.java b/src/class10/Code02_BFS.java
new file mode 100644
index 0000000..cb87d5e
--- /dev/null
+++ b/src/class10/Code02_BFS.java
@@ -0,0 +1,30 @@
+package class10;
+
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.Queue;
+
+public class Code02_BFS {
+
+	// 从node出发，进行宽度优先遍历
+	public static void bfs(Node node) {
+		if (node == null) {
+			return;
+		}
+		Queue<Node> queue = new LinkedList<>();
+		HashSet<Node> set = new HashSet<>();
+		queue.add(node);
+		set.add(node);
+		while (!queue.isEmpty()) {
+			Node cur = queue.poll();
+			System.out.println(cur.value);
+			for (Node next : cur.nexts) {
+				if (!set.contains(next)) {
+					set.add(next);
+					queue.add(next);
+				}
+			}
+		}
+	}
+
+}
diff --git a/src/class10/Code02_DFS.java b/src/class10/Code02_DFS.java
new file mode 100644
index 0000000..6ecc3cf
--- /dev/null
+++ b/src/class10/Code02_DFS.java
@@ -0,0 +1,31 @@
+package class10;
+
+import java.util.HashSet;
+import java.util.Stack;
+
+public class Code02_DFS {
+
+	public static void dfs(Node node) {
+		if (node == null) {
+			return;
+		}
+		Stack<Node> stack = new Stack<>();
+		HashSet<Node> set = new HashSet<>();
+		stack.add(node);
+		set.add(node);
+		System.out.println(node.value);
+		while (!stack.isEmpty()) {
+			Node cur = stack.pop();
+			for (Node next : cur.nexts) {
+				if (!set.contains(next)) {
+					stack.push(cur);
+					stack.push(next);
+					set.add(next);
+					System.out.println(next.value);
+					break;
+				}
+			}
+		}
+	}
+
+}
diff --git a/src/class10/Code03_TopologySort.java b/src/class10/Code03_TopologySort.java
new file mode 100644
index 0000000..51ba075
--- /dev/null
+++ b/src/class10/Code03_TopologySort.java
@@ -0,0 +1,38 @@
+package class10;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Queue;
+
+public class Code03_TopologySort {
+
+	// directed graph and no loop
+	public static List<Node> sortedTopology(Graph graph) {
+		// key：某一个node
+		// value：剩余的入度
+		HashMap<Node, Integer> inMap = new HashMap<>();
+		// 入度为0的点，才能进这个队列
+		Queue<Node> zeroInQueue = new LinkedList<>();
+		for (Node node : graph.nodes.values()) {
+			inMap.put(node, node.in);
+			if (node.in == 0) {
+				zeroInQueue.add(node);
+			}
+		}
+		// 拓扑排序的结果，依次加入result
+		List<Node> result = new ArrayList<>();
+		while (!zeroInQueue.isEmpty()) {
+			Node cur = zeroInQueue.poll();
+			result.add(cur);
+			for (Node next : cur.nexts) {
+				inMap.put(next, inMap.get(next) - 1);
+				if (inMap.get(next) == 0) {
+					zeroInQueue.add(next);
+				}
+			}
+		}
+		return result;
+	}
+}
diff --git a/src/class10/Code04_Kruskal.java b/src/class10/Code04_Kruskal.java
new file mode 100644
index 0000000..caa1da0
--- /dev/null
+++ b/src/class10/Code04_Kruskal.java
@@ -0,0 +1,142 @@
+package class10;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.PriorityQueue;
+import java.util.Set;
+import java.util.Stack;
+
+//undirected graph only
+public class Code04_Kruskal {
+	
+	public static class MySets{
+		public HashMap<Node, List<Node>>  setMap;
+		public MySets(List<Node> nodes) {
+			for(Node cur : nodes) {
+				List<Node> set = new ArrayList<Node>();
+				set.add(cur);
+				setMap.put(cur, set);
+			}
+		}
+		
+		
+		public boolean isSameSet(Node from, Node to) {
+			List<Node> fromSet  = setMap.get(from);
+			List<Node> toSet = setMap.get(to);
+			return fromSet == toSet;
+		}
+		
+		
+		public void union(Node from, Node to) {
+			List<Node> fromSet  = setMap.get(from);
+			List<Node> toSet = setMap.get(to);
+			for(Node toNode : toSet) {
+				fromSet.add(toNode);
+				setMap.put(toNode, fromSet);
+			}
+		}
+	}
+	
+	
+	
+	
+	
+	
+	
+	
+	
+	
+	
+	
+	
+	// Union-Find Set
+	public static class UnionFind {
+		// key 某一个节点， value key节点往上的节点
+		private HashMap<Node, Node> fatherMap;
+		// key 某一个集合的代表节点, value key所在集合的节点个数
+		private HashMap<Node, Integer> sizeMap;
+
+		public UnionFind() {
+			fatherMap = new HashMap<Node, Node>();
+			sizeMap = new HashMap<Node, Integer>();
+		}
+		
+		public void makeSets(Collection<Node> nodes) {
+			fatherMap.clear();
+			sizeMap.clear();
+			for (Node node : nodes) {
+				fatherMap.put(node, node);
+				sizeMap.put(node, 1);
+			}
+		}
+
+		private Node findFather(Node n) {
+			Stack<Node> path = new Stack<>();
+			while(n != fatherMap.get(n)) {
+				path.add(n);
+				n = fatherMap.get(n);
+			}
+			while(!path.isEmpty()) {
+				fatherMap.put(path.pop(), n);
+			}
+			return n;
+		}
+
+		public boolean isSameSet(Node a, Node b) {
+			return findFather(a) == findFather(b);
+		}
+
+		public void union(Node a, Node b) {
+			if (a == null || b == null) {
+				return;
+			}
+			Node aDai = findFather(a);
+			Node bDai = findFather(b);
+			if (aDai != bDai) {
+				int aSetSize = sizeMap.get(aDai);
+				int bSetSize = sizeMap.get(bDai);
+				if (aSetSize <= bSetSize) {
+					fatherMap.put(aDai, bDai);
+					sizeMap.put(bDai, aSetSize + bSetSize);
+					sizeMap.remove(aDai);
+				} else {
+					fatherMap.put(bDai, aDai);
+					sizeMap.put(aDai, aSetSize + bSetSize);
+					sizeMap.remove(bDai);
+				}
+			}
+		}
+	}
+	
+
+	public static class EdgeComparator implements Comparator<Edge> {
+
+		@Override
+		public int compare(Edge o1, Edge o2) {
+			return o1.weight - o2.weight;
+		}
+
+	}
+
+	public static Set<Edge> kruskalMST(Graph graph) {
+		UnionFind unionFind = new UnionFind();
+		unionFind.makeSets(graph.nodes.values());
+		PriorityQueue<Edge> priorityQueue = new PriorityQueue<>(new EdgeComparator());
+		for (Edge edge : graph.edges) { // M 条边
+			priorityQueue.add(edge);  // O(logM)
+		}
+		Set<Edge> result = new HashSet<>();
+		while (!priorityQueue.isEmpty()) { // M 条边
+			Edge edge = priorityQueue.poll(); // O(logM)
+			if (!unionFind.isSameSet(edge.from, edge.to)) { // O(1)
+				result.add(edge);
+				unionFind.union(edge.from, edge.to);
+			}
+		}
+		return result;
+	}
+}
diff --git a/src/class10/Code05_Prim.java b/src/class10/Code05_Prim.java
new file mode 100644
index 0000000..def87d6
--- /dev/null
+++ b/src/class10/Code05_Prim.java
@@ -0,0 +1,89 @@
+package class10;
+
+import java.util.Comparator;
+import java.util.HashSet;
+import java.util.PriorityQueue;
+import java.util.Set;
+
+// undirected graph only
+public class Code05_Prim {
+
+	public static class EdgeComparator implements Comparator<Edge> {
+
+		@Override
+		public int compare(Edge o1, Edge o2) {
+			return o1.weight - o2.weight;
+		}
+
+	}
+
+	public static Set<Edge> primMST(Graph graph) {
+		// 解锁的边进入小根堆
+		PriorityQueue<Edge> priorityQueue = new PriorityQueue<>(
+				new EdgeComparator());
+		HashSet<Node> set = new HashSet<>();
+		Set<Edge> result = new HashSet<>(); // 依次挑选的的边在result里
+		for (Node node : graph.nodes.values()) { // 随便挑了一个点
+			// node 是开始点
+			if (!set.contains(node)) {
+				set.add(node);
+				for (Edge edge : node.edges) { // 由一个点，解锁所有相连的边
+					priorityQueue.add(edge);
+				}
+				while (!priorityQueue.isEmpty()) {
+					Edge edge = priorityQueue.poll(); // 弹出解锁的边中，最小的边
+					Node toNode = edge.to; // 可能的一个新的点
+					if (!set.contains(toNode)) { // 不含有的时候，就是新的点
+						set.add(toNode);
+						result.add(edge);
+						for (Edge nextEdge : toNode.edges) {
+							priorityQueue.add(nextEdge);
+						}
+					}
+				}
+			}
+			//break;
+		}
+		return result;
+	}
+
+	// 请保证graph是连通图
+	// graph[i][j]表示点i到点j的距离，如果是系统最大值代表无路
+	// 返回值是最小连通图的路径之和
+	public static int prim(int[][] graph) {
+		int size = graph.length;
+		int[] distances = new int[size];
+		boolean[] visit = new boolean[size];
+		visit[0] = true;
+		for (int i = 0; i < size; i++) {
+			distances[i] = graph[0][i];
+		}
+		int sum = 0;
+		for (int i = 1; i < size; i++) {
+			int minPath = Integer.MAX_VALUE;
+			int minIndex = -1;
+			for (int j = 0; j < size; j++) {
+				if (!visit[j] && distances[j] < minPath) {
+					minPath = distances[j];
+					minIndex = j;
+				}
+			}
+			if (minIndex == -1) {
+				return sum;
+			}
+			visit[minIndex] = true;
+			sum += minPath;
+			for (int j = 0; j < size; j++) {
+				if (!visit[j] && distances[j] > graph[minIndex][j]) {
+					distances[j] = graph[minIndex][j];
+				}
+			}
+		}
+		return sum;
+	}
+
+	public static void main(String[] args) {
+		System.out.println("hello world!");
+	}
+
+}
diff --git a/src/class10/Code06_Dijkstra.java b/src/class10/Code06_Dijkstra.java
new file mode 100644
index 0000000..ed66369
--- /dev/null
+++ b/src/class10/Code06_Dijkstra.java
@@ -0,0 +1,163 @@
+package class10;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map.Entry;
+
+// no negative weight
+public class Code06_Dijkstra {
+
+	public static HashMap<Node, Integer> dijkstra1(Node head) {
+		// 从head出发到所有点的最小距离
+		// key : 从head出发到达key
+		// value : 从head出发到达key的最小距离
+		// 如果在表中，没有T的记录，含义是从head出发到T这个点的距离为正无穷
+		HashMap<Node, Integer> distanceMap = new HashMap<>();
+		distanceMap.put(head, 0);
+		// 已经求过距离的节点，存在selectedNodes中，以后再也不碰
+		HashSet<Node> selectedNodes = new HashSet<>();
+		Node minNode = getMinDistanceAndUnselectedNode(distanceMap, selectedNodes);
+		while (minNode != null) {
+			int distance = distanceMap.get(minNode);
+			for (Edge edge : minNode.edges) {
+				Node toNode = edge.to;
+				if (!distanceMap.containsKey(toNode)) {
+					distanceMap.put(toNode, distance + edge.weight);
+				} else {
+					distanceMap.put(edge.to, Math.min(distanceMap.get(toNode), distance + edge.weight));
+				}
+			}
+			selectedNodes.add(minNode);
+			minNode = getMinDistanceAndUnselectedNode(distanceMap, selectedNodes);
+		}
+		return distanceMap;
+	}
+
+	public static Node getMinDistanceAndUnselectedNode(HashMap<Node, Integer> distanceMap, HashSet<Node> touchedNodes) {
+		Node minNode = null;
+		int minDistance = Integer.MAX_VALUE;
+		for (Entry<Node, Integer> entry : distanceMap.entrySet()) {
+			Node node = entry.getKey();
+			int distance = entry.getValue();
+			if (!touchedNodes.contains(node) && distance < minDistance) {
+				minNode = node;
+				minDistance = distance;
+			}
+		}
+		return minNode;
+	}
+
+	public static class NodeRecord {
+		public Node node;
+		public int distance;
+
+		public NodeRecord(Node node, int distance) {
+			this.node = node;
+			this.distance = distance;
+		}
+	}
+
+	public static class NodeHeap {
+		private Node[] nodes; // 实际的堆结构
+		// key 某一个node， value 上面数组中的位置
+		private HashMap<Node, Integer> heapIndexMap;
+		// key 某一个节点， value 从源节点出发到该节点的目前最小距离
+		private HashMap<Node, Integer> distanceMap;
+		private int size; // 堆上有多少个点
+
+		public NodeHeap(int size) {
+			nodes = new Node[size];
+			heapIndexMap = new HashMap<>();
+			distanceMap = new HashMap<>();
+			size = 0;
+		}
+
+		public boolean isEmpty() {
+			return size == 0;
+		}
+
+		// 有一个点叫node，现在发现了一个从源节点出发到达node的距离为distance
+		// 判断要不要更新，如果需要的话，就更新
+		public void addOrUpdateOrIgnore(Node node, int distance) {
+			if (inHeap(node)) {
+				distanceMap.put(node, Math.min(distanceMap.get(node), distance));
+				insertHeapify(node, heapIndexMap.get(node));
+			}
+			if (!isEntered(node)) {
+				nodes[size] = node;
+				heapIndexMap.put(node, size);
+				distanceMap.put(node, distance);
+				insertHeapify(node, size++);
+			}
+		}
+
+		public NodeRecord pop() {
+			NodeRecord nodeRecord = new NodeRecord(nodes[0], distanceMap.get(nodes[0]));
+			swap(0, size - 1);
+			heapIndexMap.put(nodes[size - 1], -1);
+			distanceMap.remove(nodes[size - 1]);
+			// free C++同学还要把原本堆顶节点析构，对java同学不必
+			nodes[size - 1] = null;
+			heapify(0, --size);
+			return nodeRecord;
+		}
+
+		private void insertHeapify(Node node, int index) {
+			while (distanceMap.get(nodes[index]) < distanceMap.get(nodes[(index - 1) / 2])) {
+				swap(index, (index - 1) / 2);
+				index = (index - 1) / 2;
+			}
+		}
+
+		private void heapify(int index, int size) {
+			int left = index * 2 + 1;
+			while (left < size) {
+				int smallest = left + 1 < size && distanceMap.get(nodes[left + 1]) < distanceMap.get(nodes[left])
+						? left + 1
+						: left;
+				smallest = distanceMap.get(nodes[smallest]) < distanceMap.get(nodes[index]) ? smallest : index;
+				if (smallest == index) {
+					break;
+				}
+				swap(smallest, index);
+				index = smallest;
+				left = index * 2 + 1;
+			}
+		}
+
+		private boolean isEntered(Node node) {
+			return heapIndexMap.containsKey(node);
+		}
+
+		private boolean inHeap(Node node) {
+			return isEntered(node) && heapIndexMap.get(node) != -1;
+		}
+
+		private void swap(int index1, int index2) {
+			heapIndexMap.put(nodes[index1], index2);
+			heapIndexMap.put(nodes[index2], index1);
+			Node tmp = nodes[index1];
+			nodes[index1] = nodes[index2];
+			nodes[index2] = tmp;
+		}
+	}
+
+	// 改进后的dijkstra算法
+	// 从head出发，所有head能到达的节点，生成到达每个节点的最小路径记录并返回
+	public static HashMap<Node, Integer> dijkstra2(Node head, int size) {
+		NodeHeap nodeHeap = new NodeHeap(size);
+		nodeHeap.addOrUpdateOrIgnore(head, 0);
+		HashMap<Node, Integer> result = new HashMap<>();
+		while (!nodeHeap.isEmpty()) {
+			NodeRecord record = nodeHeap.pop();
+			Node cur = record.node;
+			int distance = record.distance;
+			for (Edge edge : cur.edges) {
+				nodeHeap.addOrUpdateOrIgnore(edge.to, edge.weight + distance);
+			}
+			result.put(cur, distance);
+		}
+		return result;
+	}
+
+}
diff --git a/src/class10/Edge.java b/src/class10/Edge.java
new file mode 100644
index 0000000..8786552
--- /dev/null
+++ b/src/class10/Edge.java
@@ -0,0 +1,14 @@
+package class10;
+
+public class Edge {
+	public int weight;
+	public Node from;
+	public Node to;
+
+	public Edge(int weight, Node from, Node to) {
+		this.weight = weight;
+		this.from = from;
+		this.to = to;
+	}
+
+}
diff --git a/src/class10/Graph.java b/src/class10/Graph.java
new file mode 100644
index 0000000..484504f
--- /dev/null
+++ b/src/class10/Graph.java
@@ -0,0 +1,14 @@
+package class10;
+
+import java.util.HashMap;
+import java.util.HashSet;
+
+public class Graph {
+	public HashMap<Integer, Node> nodes;
+	public HashSet<Edge> edges;
+
+	public Graph() {
+		nodes = new HashMap<>();
+		edges = new HashSet<>();
+	}
+}
diff --git a/src/class10/GraphGenerator.java b/src/class10/GraphGenerator.java
new file mode 100644
index 0000000..dc6a0b8
--- /dev/null
+++ b/src/class10/GraphGenerator.java
@@ -0,0 +1,32 @@
+package class10;
+
+public class GraphGenerator {
+
+	// matrix 所有的边
+	// N*3 的矩阵
+	// [weight, from节点上面的值，to节点上面的值]
+	public static Graph createGraph(Integer[][] matrix) {
+		Graph graph = new Graph();
+		for (int i = 0; i < matrix.length; i++) { // matrix[0][0], matrix[0][1]  matrix[0][2]
+			Integer from = matrix[i][0];
+			Integer to = matrix[i][1];
+			Integer weight = matrix[i][2];
+			if (!graph.nodes.containsKey(from)) {
+				graph.nodes.put(from, new Node(from));
+			}
+			if (!graph.nodes.containsKey(to)) {
+				graph.nodes.put(to, new Node(to));
+			}
+			Node fromNode = graph.nodes.get(from);
+			Node toNode = graph.nodes.get(to);
+			Edge newEdge = new Edge(weight, fromNode, toNode);
+			fromNode.nexts.add(toNode);
+			fromNode.out++;
+			toNode.in++;
+			fromNode.edges.add(newEdge);
+			graph.edges.add(newEdge);
+		}
+		return graph;
+	}
+
+}
diff --git a/src/class10/Node.java b/src/class10/Node.java
new file mode 100644
index 0000000..f56e977
--- /dev/null
+++ b/src/class10/Node.java
@@ -0,0 +1,19 @@
+package class10;
+
+import java.util.ArrayList;
+
+public class Node {
+	public int value;
+	public int in;
+	public int out;
+	public ArrayList<Node> nexts;
+	public ArrayList<Edge> edges;
+
+	public Node(int value) {
+		this.value = value;
+		in = 0;
+		out = 0;
+		nexts = new ArrayList<>();
+		edges = new ArrayList<>();
+	}
+}
diff --git a/src/class11/Code01_Hanoi.java b/src/class11/Code01_Hanoi.java
new file mode 100644
index 0000000..b840f8b
--- /dev/null
+++ b/src/class11/Code01_Hanoi.java
@@ -0,0 +1,94 @@
+package class11;
+
+public class Code01_Hanoi {
+
+	public static void hanoi1(int n) {
+		leftToRight(n);
+	}
+
+	public static void leftToRight(int n) {
+		if (n == 1) {
+			System.out.println("Move 1 from left to right");
+			return;
+		}
+		leftToMid(n - 1);
+		System.out.println("Move " + n + " from left to right");
+		midToRight(n - 1);
+	}
+
+	public static void leftToMid(int n) {
+		if (n == 1) {
+			System.out.println("Move 1 from left to mid");
+			return;
+		}
+		leftToRight(n - 1);
+		System.out.println("Move " + n + " from left to mid");
+		rightToMid(n - 1);
+	}
+
+	public static void rightToMid(int n) {
+		if (n == 1) {
+			System.out.println("Move 1 from right to mid");
+			return;
+		}
+		rightToLeft(n - 1);
+		System.out.println("Move " + n + " from right to mid");
+		leftToMid(n - 1);
+	}
+
+	public static void midToRight(int n) {
+		if (n == 1) {
+			System.out.println("Move 1 from mid to right");
+			return;
+		}
+		midToLeft(n - 1);
+		System.out.println("Move " + n + " from mid to right");
+		leftToRight(n - 1);
+	}
+
+	public static void midToLeft(int n) {
+		if (n == 1) {
+			System.out.println("Move 1 from mid to left");
+			return;
+		}
+		midToRight(n - 1);
+		System.out.println("Move " + n + " from mid to left");
+		rightToLeft(n - 1);
+	}
+
+	public static void rightToLeft(int n) {
+		if (n == 1) {
+			System.out.println("Move 1 from right to left");
+			return;
+		}
+		rightToMid(n - 1);
+		System.out.println("Move " + n + " from right to left");
+		midToLeft(n - 1);
+	}
+
+	public static void hanoi2(int n) {
+		if (n > 0) {
+			func(n, "left", "right", "mid");
+		}
+	}
+
+	// 1~i 圆盘 目标是from -> to， other是另外一个
+	public static void func(int N, String from, String to, String other) {
+		if (N == 1) { // base
+			System.out.println("Move 1 from " + from + " to " + to);
+		} else {
+			func(N - 1, from, other, to);
+			System.out.println("Move " + N + " from " + from + " to " + to);
+			func(N - 1, other, to, from);
+		}
+	}
+
+	public static void main(String[] args) {
+		int n = 3;
+		hanoi1(n);
+		System.out.println("============");
+		hanoi2(n);
+		System.out.println("============");
+	}
+
+}
diff --git a/src/class11/Code02_PrintAllSubsquences.java b/src/class11/Code02_PrintAllSubsquences.java
new file mode 100644
index 0000000..fd5e896
--- /dev/null
+++ b/src/class11/Code02_PrintAllSubsquences.java
@@ -0,0 +1,67 @@
+package class11;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+
+public class Code02_PrintAllSubsquences {
+
+	public static List<String> subs(String s) {
+		char[] str = s.toCharArray();
+		String path = "";
+		List<String> ans = new ArrayList<>();
+		process1(str, 0, ans, path);
+		return ans;
+	}
+
+	public static void process1(char[] str, int index, List<String> ans, String path) {
+		if (index == str.length) {
+			ans.add(path);
+			return;
+		}
+		String no = path;
+		process1(str, index + 1, ans, no);
+		String yes = path + String.valueOf(str[index]);
+		process1(str, index + 1, ans, yes);
+	}
+
+	public static List<String> subsNoRepeat(String s) {
+		char[] str = s.toCharArray();
+		String path = "";
+		HashSet<String> set = new HashSet<>();
+		process2(str, 0, set, path);
+		List<String> ans = new ArrayList<>();
+		for (String cur : set) {
+			ans.add(cur);
+		}
+		return ans;
+	}
+
+	public static void process2(char[] str, int index, HashSet<String> set, String path) {
+		if (index == str.length) {
+			set.add(path);
+			return;
+		}
+		String no = path;
+		process2(str, index + 1, set, no);
+		String yes = path + String.valueOf(str[index]);
+		process2(str, index + 1, set, yes);
+	}
+
+	public static void main(String[] args) {
+		String test = "aacc";
+		List<String> ans1 = subs(test);
+		List<String> ans2 = subsNoRepeat(test);
+
+		for (String str : ans1) {
+			System.out.println(str);
+		}
+		System.out.println("=================");
+		for (String str : ans2) {
+			System.out.println(str);
+		}
+		System.out.println("=================");
+
+	}
+
+}
diff --git a/src/class11/Code03_PrintAllPermutations.java b/src/class11/Code03_PrintAllPermutations.java
new file mode 100644
index 0000000..7a8a589
--- /dev/null
+++ b/src/class11/Code03_PrintAllPermutations.java
@@ -0,0 +1,74 @@
+package class11;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Code03_PrintAllPermutations {
+
+	public static ArrayList<String> permutation(String str) {
+		ArrayList<String> res = new ArrayList<>();
+		if (str == null || str.length() == 0) {
+			return res;
+		}
+		char[] chs = str.toCharArray();
+		process(chs, 0, res);
+		return res;
+	}
+
+	public static void process(char[] str, int i, ArrayList<String> res) {
+		if (i == str.length) {
+			res.add(String.valueOf(str));
+		}
+		for (int j = i; j < str.length; j++) {
+			swap(str, i, j);
+			process(str, i + 1, res);
+			swap(str, i, j);
+		}
+	}
+
+	public static ArrayList<String> permutationNoRepeat(String str) {
+		ArrayList<String> res = new ArrayList<>();
+		if (str == null || str.length() == 0) {
+			return res;
+		}
+		char[] chs = str.toCharArray();
+		process2(chs, 0, res);
+		return res;
+	}
+
+	public static void process2(char[] str, int i, ArrayList<String> res) {
+		if (i == str.length) {
+			res.add(String.valueOf(str));
+		}
+		boolean[] visit = new boolean[26]; // visit[0 1 .. 25]
+		for (int j = i; j < str.length; j++) {
+			if (!visit[str[j] - 'a']) {
+				visit[str[j] - 'a'] = true;
+				swap(str, i, j);
+				process2(str, i + 1, res);
+				swap(str, i, j);
+			}
+		}
+	}
+
+	public static void swap(char[] chs, int i, int j) {
+		char tmp = chs[i];
+		chs[i] = chs[j];
+		chs[j] = tmp;
+	}
+
+	public static void main(String[] args) {
+		String s = "aac";
+		List<String> ans1 = permutation(s);
+		for (String str : ans1) {
+			System.out.println(str);
+		}
+		System.out.println("=======");
+		List<String> ans2 = permutationNoRepeat(s);
+		for (String str : ans2) {
+			System.out.println(str);
+		}
+
+	}
+
+}
diff --git a/src/class11/Code04_ReverseStackUsingRecursive.java b/src/class11/Code04_ReverseStackUsingRecursive.java
new file mode 100644
index 0000000..8e9134c
--- /dev/null
+++ b/src/class11/Code04_ReverseStackUsingRecursive.java
@@ -0,0 +1,41 @@
+package class11;
+
+import java.util.Stack;
+
+public class Code04_ReverseStackUsingRecursive {
+
+	public static void reverse(Stack<Integer> stack) {
+		if (stack.isEmpty()) {
+			return;
+		}
+		int i = f(stack);
+		reverse(stack);
+		stack.push(i);
+	}
+
+	public static int f(Stack<Integer> stack) {
+		int result = stack.pop();
+		if (stack.isEmpty()) {
+			return result;
+		} else {
+			int last = f(stack);
+			stack.push(result);
+			return last;
+		}
+	}
+
+	public static void main(String[] args) {
+		Stack<Integer> test = new Stack<Integer>();
+		test.push(1);
+		test.push(2);
+		test.push(3);
+		test.push(4);
+		test.push(5);
+		reverse(test);
+		while (!test.isEmpty()) {
+			System.out.println(test.pop());
+		}
+
+	}
+
+}
diff --git a/src/class11/Code06_ConvertToLetterString.java b/src/class11/Code06_ConvertToLetterString.java
new file mode 100644
index 0000000..1a21ffa
--- /dev/null
+++ b/src/class11/Code06_ConvertToLetterString.java
@@ -0,0 +1,74 @@
+package class11;
+
+public class Code06_ConvertToLetterString {
+
+	public static int number(String str) {
+		if (str == null || str.length() == 0) {
+			return 0;
+		}
+		return process(str.toCharArray(), 0);
+	}
+
+	// i之前的位置，如何转化已经做过决定了, 不用再关心
+	// i... 有多少种转化的结果
+	public static int process(char[] str, int i) {
+		if (i == str.length) { // base case
+			return 1;
+		}
+		// i没有到终止位置
+		if (str[i] == '0') {
+			return 0;
+		}
+		// str[i]字符不是‘0’
+		if (str[i] == '1') {
+			int res = process(str, i + 1); // i自己作为单独的部分，后续有多少种方法
+			if (i + 1 < str.length) {
+				res += process(str, i + 2); // (i和i+1)作为单独的部分，后续有多少种方法
+			}
+			return res;
+		}
+		if (str[i] == '2') {
+			int res = process(str, i + 1); // i自己作为单独的部分，后续有多少种方法
+			// (i和i+1)作为单独的部分并且没有超过26，后续有多少种方法
+			if (i + 1 < str.length && (str[i + 1] >= '0' && str[i + 1] <= '6')) {
+				res += process(str, i + 2); // (i和i+1)作为单独的部分，后续有多少种方法
+			}
+			return res;
+		}
+		// str[i] == '3' ~ '9'
+		return process(str, i + 1);
+	}
+
+	public static int dpWays(String s) {
+		if (s == null || s.length() == 0) {
+			return 0;
+		}
+		char[] str = s.toCharArray();
+		int N = str.length;
+		int[] dp = new int[N + 1];
+		dp[N] = 1;
+		for (int i = N - 1; i >= 0; i--) {
+			if (str[i] == '0') {
+				dp[i] = 0;
+			} else if (str[i] == '1') {
+				dp[i] = dp[i + 1];
+				if (i + 1 < N) {
+					dp[i] += dp[i + 2];
+				}
+			} else if (str[i] == '2') {
+				dp[i] = dp[i + 1]; 
+				if (i + 1 < str.length && (str[i + 1] >= '0' && str[i + 1] <= '6')) {
+					dp[i] += dp[i + 2];
+				}
+			} else {
+				dp[i] = dp[i + 1];
+			}
+		}
+		return dp[0];
+	}
+
+	public static void main(String[] args) {
+		System.out.println(number("11111"));
+	}
+
+}
diff --git a/src/class11/Code07_Knapsack.java b/src/class11/Code07_Knapsack.java
new file mode 100644
index 0000000..6ae4b46
--- /dev/null
+++ b/src/class11/Code07_Knapsack.java
@@ -0,0 +1,74 @@
+package class11;
+
+public class Code07_Knapsack {
+
+	public static int getMaxValue(int[] w, int[] v, int bag) {
+		return process(w, v, 0, 0, bag);
+	}
+
+	// index... 最大价值
+	public static int process(int[] w, int[] v, int index, int alreadyW, int bag) {
+		if (alreadyW > bag) {
+			return -1;
+		}
+		// 重量没超
+		if (index == w.length) {
+			return 0;
+		}
+		int p1 = process(w, v, index + 1, alreadyW, bag);
+		int p2next = process(w, v, index + 1, alreadyW + w[index], bag);
+		int p2 = -1;
+		if (p2next != -1) {
+			p2 = v[index] + p2next;
+		}
+		return Math.max(p1, p2);
+
+	}
+
+	public static int maxValue(int[] w, int[] v, int bag) {
+		return process(w, v, 0, bag);
+	}
+
+	// 只剩下rest的空间了，
+	// index...货物自由选择，但是不要超过rest的空间
+	// 返回能够获得的最大价值
+	public static int process(int[] w, int[] v, int index, int rest) {
+		if (rest <= 0) { // base case 1
+			return 0;
+		}
+		// rest >=0
+		if (index == w.length) { // base case 2
+			return 0;
+		}
+		// 有货也有空间
+		int p1 = process(w, v, index + 1, rest);
+		int p2 = Integer.MIN_VALUE;
+		if (rest >= w[index]) {
+			p2 = v[index] + process(w, v, index + 1, rest - w[index]);
+		}
+		return Math.max(p1, p2);
+	}
+
+	public static int dpWay(int[] w, int[] v, int bag) {
+		int N = w.length;
+		int[][] dp = new int[N + 1][bag + 1];
+		for (int index = N - 1; index >= 0; index--) {
+			for (int rest = 1; rest <= bag; rest++) {
+				dp[index][rest] = dp[index + 1][rest];
+				if (rest >= w[index]) {
+					dp[index][rest] = Math.max(dp[index][rest], v[index] + dp[index + 1][rest - w[index]]);
+				}
+			}
+		}
+		return dp[0][bag];
+	}
+
+	public static void main(String[] args) {
+		int[] weights = { 3, 2, 4, 7 };
+		int[] values = { 5, 6, 3, 19 };
+		int bag = 11;
+		System.out.println(maxValue(weights, values, bag));
+		System.out.println(dpWay(weights, values, bag));
+	}
+
+}
diff --git a/src/class11/Code08_CardsInLine.java b/src/class11/Code08_CardsInLine.java
new file mode 100644
index 0000000..7ee3451
--- /dev/null
+++ b/src/class11/Code08_CardsInLine.java
@@ -0,0 +1,49 @@
+package class11;
+
+public class Code08_CardsInLine {
+
+	public static int win1(int[] arr) {
+		if (arr == null || arr.length == 0) {
+			return 0;
+		}
+		return Math.max(f(arr, 0, arr.length - 1), s(arr, 0, arr.length - 1));
+	}
+
+	public static int f(int[] arr, int i, int j) {
+		if (i == j) {
+			return arr[i];
+		}
+		return Math.max(arr[i] + s(arr, i + 1, j), arr[j] + s(arr, i, j - 1));
+	}
+
+	public static int s(int[] arr, int i, int j) {
+		if (i == j) {
+			return 0;
+		}
+		return Math.min(f(arr, i + 1, j), f(arr, i, j - 1));
+	}
+
+	public static int win2(int[] arr) {
+		if (arr == null || arr.length == 0) {
+			return 0;
+		}
+		int[][] f = new int[arr.length][arr.length];
+		int[][] s = new int[arr.length][arr.length];
+		for (int j = 0; j < arr.length; j++) {
+			f[j][j] = arr[j];
+			for (int i = j - 1; i >= 0; i--) {
+				f[i][j] = Math.max(arr[i] + s[i + 1][j], arr[j] + s[i][j - 1]);
+				s[i][j] = Math.min(f[i + 1][j], f[i][j - 1]);
+			}
+		}
+		return Math.max(f[0][arr.length - 1], s[0][arr.length - 1]);
+	}
+
+	public static void main(String[] args) {
+		int[] arr = { 1, 9, 1 };
+		System.out.println(win1(arr));
+		System.out.println(win2(arr));
+
+	}
+
+}
diff --git a/src/class11/Code09_NQueens.java b/src/class11/Code09_NQueens.java
new file mode 100644
index 0000000..357f698
--- /dev/null
+++ b/src/class11/Code09_NQueens.java
@@ -0,0 +1,95 @@
+package class11;
+
+public class Code09_NQueens {
+
+	public static int num1(int n) {
+		if (n < 1) {
+			return 0;
+		}
+		// record[0] ?  record[1]  ?  record[2]
+		int[] record = new int[n]; // record[i] -> i行的皇后，放在了第几列
+		return process1(0, record, n);
+	}
+
+	// 潜台词：record[0..i-1]的皇后，任何两个皇后一定都不共行、不共列，不共斜线
+	// 目前来到了第i行
+	// record[0..i-1]表示之前的行，放了的皇后位置
+	// n代表整体一共有多少行
+	// 返回值是，摆完所有的皇后，合理的摆法有多少种
+	public static int process1(int i, int[] record, int n) {
+		if (i == n) { // 终止行
+			return 1;
+		}
+		int res = 0;
+		for (int j = 0; j < n; j++) { // 当前行在i行，尝试i行所有的列  -> j
+			// 当前i行的皇后，放在j列，会不会和之前(0..i-1)的皇后，不共行共列或者共斜线，
+			// 如果是，认为有效
+			// 如果不是，认为无效
+			if (isValid(record, i, j)) {
+				record[i] = j;
+				res += process1(i + 1, record, n);
+			}
+		}
+		return res;
+	}
+
+	// record[0..i-1]你需要看，record[i...]不需要看
+	// 返回i行皇后，放在了j列，是否有效
+	public static boolean isValid(int[] record, int i, int j) {
+		for (int k = 0; k < i; k++) { // 之前的某个k行的皇后
+			if (j == record[k] || Math.abs(record[k] - j) == Math.abs(i - k)) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	// 请不要超过32皇后问题
+	public static int num2(int n) {
+		if (n < 1 || n > 32) {
+			return 0;
+		}
+		int limit = n == 32 ? -1 : (1 << n) - 1;
+		return process2(limit, 0, 0, 0);
+	}
+
+	// colLim 列的限制，1的位置不能放皇后，0的位置可以
+	// leftDiaLim 左斜线的限制，1的位置不能放皇后，0的位置可以
+	// rightDiaLim 右斜线的限制，1的位置不能放皇后，0的位置可以
+	public static int process2(int limit, 
+			int colLim, 
+			int leftDiaLim,
+			int rightDiaLim) {
+		if (colLim == limit) { // base case
+			return 1;
+		}
+		// 所有候选皇后的位置，都在pos上
+		int pos = limit & (~(colLim | leftDiaLim | rightDiaLim));
+		int mostRightOne = 0;
+		int res = 0;
+		while (pos != 0) {
+			mostRightOne = pos & (~pos + 1);
+			pos = pos - mostRightOne;
+			res += process2(limit, 
+					colLim | mostRightOne,
+					(leftDiaLim | mostRightOne) << 1,
+					(rightDiaLim | mostRightOne) >>> 1);
+		}
+		return res;
+	}
+
+	public static void main(String[] args) {
+		int n = 14;
+
+		long start = System.currentTimeMillis();
+		System.out.println(num2(n));
+		long end = System.currentTimeMillis();
+		System.out.println("cost time: " + (end - start) + "ms");
+
+		start = System.currentTimeMillis();
+		System.out.println(num1(n));
+		end = System.currentTimeMillis();
+		System.out.println("cost time: " + (end - start) + "ms");
+
+	}
+}
diff --git a/src/class12/Code01_RobotWalk.java b/src/class12/Code01_RobotWalk.java
new file mode 100644
index 0000000..ef8bcd3
--- /dev/null
+++ b/src/class12/Code01_RobotWalk.java
@@ -0,0 +1,139 @@
+package class12;
+
+public class Code01_RobotWalk {
+
+	public static int ways1(int N, int M, int K, int P) {
+		// 参数无效直接返回0
+		if (N < 2 || K < 1 || M < 1 || M > N || P < 1 || P > N) {
+			return 0;
+		}
+		// 总共N个位置，从M点出发，还剩K步，返回最终能达到P的方法数
+		return walk(N, M, K, P);
+	}
+
+	// N : 位置为1 ~ N，固定参数
+	// cur : 当前在cur位置，可变参数
+	// rest : 还剩res步没有走，可变参数
+	// P : 最终目标位置是P，固定参数
+	// 该函数的含义：只能在1~N这些位置上移动，当前在cur位置，走完rest步之后，停在P位置的方法数作为返回值返回
+	public static int walk(int N, int cur, int rest, int P) {
+		// 如果没有剩余步数了，当前的cur位置就是最后的位置
+		// 如果最后的位置停在P上，那么之前做的移动是有效的
+		// 如果最后的位置没在P上，那么之前做的移动是无效的
+		if (rest == 0) {
+			return cur == P ? 1 : 0;
+		}
+		// 如果还有rest步要走，而当前的cur位置在1位置上，那么当前这步只能从1走向2
+		// 后续的过程就是，来到2位置上，还剩rest-1步要走
+		if (cur == 1) {
+			return walk(N, 2, rest - 1, P);
+		}
+		// 如果还有rest步要走，而当前的cur位置在N位置上，那么当前这步只能从N走向N-1
+		// 后续的过程就是，来到N-1位置上，还剩rest-1步要走
+		if (cur == N) {
+			return walk(N, N - 1, rest - 1, P);
+		}
+		// 如果还有rest步要走，而当前的cur位置在中间位置上，那么当前这步可以走向左，也可以走向右
+		// 走向左之后，后续的过程就是，来到cur-1位置上，还剩rest-1步要走
+		// 走向右之后，后续的过程就是，来到cur+1位置上，还剩rest-1步要走
+		// 走向左、走向右是截然不同的方法，所以总方法数要都算上
+		return walk(N, cur + 1, rest - 1, P) + walk(N, cur - 1, rest - 1, P);
+	}
+
+	public static int ways2(int N, int M, int K, int P) {
+		// 参数无效直接返回0
+		if (N < 2 || K < 1 || M < 1 || M > N || P < 1 || P > N) {
+			return 0;
+		}
+		int[][] dp = new int[K + 1][N + 1];
+		dp[0][P] = 1;
+		for (int i = 1; i <= K; i++) {
+			for (int j = 1; j <= N; j++) {
+				if (j == 1) {
+					dp[i][j] = dp[i - 1][2];
+				} else if (j == N) {
+					dp[i][j] = dp[i - 1][N - 1];
+				} else {
+					dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j + 1];
+				}
+			}
+		}
+		return dp[K][M];
+	}
+
+	public static int ways3(int N, int M, int K, int P) {
+		// 参数无效直接返回0
+		if (N < 2 || K < 1 || M < 1 || M > N || P < 1 || P > N) {
+			return 0;
+		}
+		int[] dp = new int[N + 1];
+		dp[P] = 1;
+		for (int i = 1; i <= K; i++) {
+			int leftUp = dp[1];// 左上角的值
+			for (int j = 1; j <= N; j++) {
+				int tmp = dp[j];
+				if (j == 1) {
+					dp[j] = dp[j + 1];
+				} else if (j == N) {
+					dp[j] = leftUp;
+				} else {
+					dp[j] = leftUp + dp[j + 1];
+				}
+				leftUp = tmp;
+			}
+		}
+		return dp[M];
+	}
+
+	// ways4是你的方法
+	public static int ways4(int N, int M, int K, int P) {
+		if (N < 2 || K < 1 || M < 1 || M > N || P < 1 || P > N) {
+			return 0;
+		}
+		return process(N, 0, P, M, K);
+	}
+
+	// 一共N个位置，从M点出发，一共只有K步。返回走到位置j，剩余步数为i的方法数
+	public static int process(int N, int i, int j, int M, int K) {
+		if (i == K) {
+			return j == M ? 1 : 0;
+		}
+		if (j == 1) {
+			return process(N, i + 1, j + 1, M, K);
+		}
+		if (j == N) {
+			return process(N, i + 1, j - 1, M, K);
+		}
+		return process(N, i + 1, j + 1, M, K) + process(N, i + 1, j - 1, M, K);
+	}
+
+	// ways5是你的方法的dp优化
+	public static int ways5(int N, int M, int K, int P) {
+		if (N < 2 || K < 1 || M < 1 || M > N || P < 1 || P > N) {
+			return 0;
+		}
+		int[][] dp = new int[K + 1][N + 1];
+		dp[K][M] = 1;
+		for (int i = K - 1; i >= 0; i--) {
+			for (int j = 1; j <= N; j++) {
+				if (j == 1) {
+					dp[i][j] = dp[i + 1][j + 1];
+				} else if (j == N) {
+					dp[i][j] = dp[i + 1][j - 1];
+				} else {
+					dp[i][j] = dp[i + 1][j + 1] + dp[i + 1][j - 1];
+				}
+			}
+		}
+		return dp[0][P];
+	}
+
+	public static void main(String[] args) {
+		System.out.println(ways1(7, 4, 9, 5));
+		System.out.println(ways2(7, 4, 9, 5));
+		System.out.println(ways3(7, 4, 9, 5));
+		System.out.println(ways4(7, 4, 9, 5));
+		System.out.println(ways5(7, 4, 9, 5));
+	}
+
+}
diff --git a/src/class12/Code02_StickersToSpellWord.java b/src/class12/Code02_StickersToSpellWord.java
new file mode 100644
index 0000000..34e7016
--- /dev/null
+++ b/src/class12/Code02_StickersToSpellWord.java
@@ -0,0 +1,132 @@
+package class12;
+
+import java.util.Arrays;
+import java.util.HashMap;
+
+public class Code02_StickersToSpellWord {
+
+	public static int minStickers1(String[] stickers, String target) {
+		int n = stickers.length;
+		int[][] map = new int[n][26];
+		HashMap<String, Integer> dp = new HashMap<>();
+		for (int i = 0; i < n; i++) {
+			char[] str = stickers[i].toCharArray();
+			for (char c : str) {
+				map[i][c - 'a']++;
+			}
+		}
+		dp.put("", 0);
+		return process1(dp, map, target);
+	}
+
+	// dp 傻缓存，如果t已经算过了，直接返回dp中的值
+	// t 剩余的目标
+	// 0..N每一个字符串所含字符的词频统计
+	public static int process1(HashMap<String, Integer> dp, int[][] map, String t) {
+		if (dp.containsKey(t)) {
+			return dp.get(t);
+		}
+		int ans = Integer.MAX_VALUE;
+		int n = map.length;
+		int[] tmap = new int[26];
+		char[] target = t.toCharArray();
+		for (char c : target) {
+			tmap[c - 'a']++;
+		}
+		for (int i = 0; i < n; i++) {
+			if (map[i][target[0] - 'a'] == 0) {
+				continue;
+			}
+			StringBuilder sb = new StringBuilder();
+			for (int j = 0; j < 26; j++) {
+				if (tmap[j] > 0) { // j这个字符是target需要的
+					for (int k = 0; k < Math.max(0, tmap[j] - map[i][j]); k++) {
+						sb.append((char) ('a' + j));
+					}
+				}
+			}
+			String s = sb.toString();
+			int tmp = process1(dp, map, s);
+			if (tmp != -1) {
+				ans = Math.min(ans, 1 + tmp);
+			}
+		}
+		dp.put(t, ans == Integer.MAX_VALUE ? -1 : ans);
+		return dp.get(t);
+	}
+
+	public static int minStickers2(String[] stickers, String target) {
+		int n = stickers.length;
+		int[][] map = new int[n][26];
+		for (int i = 0; i < n; i++) {
+			char[] str = stickers[i].toCharArray();
+			for (char c : str) {
+				map[i][c - 'a']++;
+			}
+		}
+		char[] str = target.toCharArray();
+		int[] tmap = new int[26];
+		for (char c : str) {
+			tmap[c - 'a']++;
+		}
+		HashMap<String, Integer> dp = new HashMap<>();
+		int ans = process2(map, 0, tmap, dp);
+		return ans;
+	}
+
+	public static int process2(int[][] map, int i, int[] tmap, HashMap<String, Integer> dp) {
+		StringBuilder keyBuilder = new StringBuilder();
+		keyBuilder.append(i + "_");
+		for (int asc = 0; asc < 26; asc++) {
+			if (tmap[asc] != 0) {
+				keyBuilder.append((char) (asc + 'a') + "_" + tmap[asc] + "_");
+			}
+		}
+		String key = keyBuilder.toString();
+		if (dp.containsKey(key)) {
+			return dp.get(key);
+		}
+		boolean finish = true;
+		for (int asc = 0; asc < 26; asc++) {
+			if (tmap[asc] != 0) {
+				finish = false;
+				break;
+			}
+		}
+		if (finish) {
+			dp.put(key, 0);
+			return 0;
+		}
+		if (i == map.length) {
+			dp.put(key, -1);
+			return -1;
+		}
+		int maxZhang = 0;
+		for (int asc = 0; asc < 26; asc++) {
+			if (map[i][asc] != 0 && tmap[asc] != 0) {
+				maxZhang = Math.max(maxZhang, (tmap[asc] / map[i][asc]) + (tmap[asc] % map[i][asc] == 0 ? 0 : 1));
+			}
+		}
+		int[] backup = Arrays.copyOf(tmap, tmap.length);
+		int min = Integer.MAX_VALUE;
+		int next = process2(map, i + 1, tmap, dp);
+		tmap = Arrays.copyOf(backup, backup.length);
+		if (next != -1) {
+			min = next;
+		}
+		for (int zhang = 1; zhang <= maxZhang; zhang++) {
+			for (int asc = 0; asc < 26; asc++) {
+				tmap[asc] = Math.max(0, tmap[asc] - (map[i][asc] * zhang));
+			}
+			next = process2(map, i + 1, tmap, dp);
+			tmap = Arrays.copyOf(backup, backup.length);
+			if (next != -1) {
+				min = Math.min(min, zhang + next);
+			}
+		}
+		int ans = min == Integer.MAX_VALUE ? -1 : min;
+		dp.put(key, ans);
+		return ans;
+	}
+
+}
diff --git a/src/class12/Code03_Knapsack.java b/src/class12/Code03_Knapsack.java
new file mode 100644
index 0000000..23c7a87
--- /dev/null
+++ b/src/class12/Code03_Knapsack.java
@@ -0,0 +1,74 @@
+package class12;
+
+public class Code03_Knapsack {
+
+	public static int getMaxValue(int[] w, int[] v, int bag) {
+		return process(w, v, 0, 0, bag);
+	}
+
+	// index... 最大价值
+	public static int process(int[] w, int[] v, int index, int alreadyW, int bag) {
+		if (alreadyW > bag) {
+			return -1;
+		}
+		// 重量没超
+		if (index == w.length) {
+			return 0;
+		}
+		int p1 = process(w, v, index + 1, alreadyW, bag);
+		int p2next = process(w, v, index + 1, alreadyW + w[index], bag);
+		int p2 = -1;
+		if (p2next != -1) {
+			p2 = v[index] + p2next;
+		}
+		return Math.max(p1, p2);
+
+	}
+
+	public static int maxValue(int[] w, int[] v, int bag) {
+		return process(w, v, 0, bag);
+	}
+
+	// 只剩下rest的空间了，
+	// index...货物自由选择，但是不要超过rest的空间
+	// 返回能够获得的最大价值
+	public static int process(int[] w, int[] v, int index, int rest) {
+		if (rest <= 0) { // base case 1
+			return 0;
+		}
+		// rest >=0
+		if (index == w.length) { // base case 2
+			return 0;
+		}
+		// 有货也有空间
+		int p1 = process(w, v, index + 1, rest);
+		int p2 = Integer.MIN_VALUE;
+		if (rest >= w[index]) {
+			p2 = v[index] + process(w, v, index + 1, rest - w[index]);
+		}
+		return Math.max(p1, p2);
+	}
+
+	public static int dpWay(int[] w, int[] v, int bag) {
+		int N = w.length;
+		int[][] dp = new int[N + 1][bag + 1];
+		for (int index = N - 1; index >= 0; index--) {
+			for (int rest = 1; rest <= bag; rest++) {
+				dp[index][rest] = dp[index + 1][rest];
+				if (rest >= w[index]) {
+					dp[index][rest] = Math.max(dp[index][rest], v[index] + dp[index + 1][rest - w[index]]);
+				}
+			}
+		}
+		return dp[0][bag];
+	}
+
+	public static void main(String[] args) {
+		int[] weights = { 3, 2, 4, 7 };
+		int[] values = { 5, 6, 3, 19 };
+		int bag = 11;
+		System.out.println(maxValue(weights, values, bag));
+		System.out.println(dpWay(weights, values, bag));
+	}
+
+}
diff --git a/src/class12/Code04_CardsInLine.java b/src/class12/Code04_CardsInLine.java
new file mode 100644
index 0000000..37ad9e4
--- /dev/null
+++ b/src/class12/Code04_CardsInLine.java
@@ -0,0 +1,61 @@
+package class12;
+
+public class Code04_CardsInLine {
+
+	public static int win1(int[] arr) {
+		if (arr == null || arr.length == 0) {
+			return 0;
+		}
+		return Math.max(f(arr, 0, arr.length - 1), s(arr, 0, arr.length - 1));
+	}
+
+	public static int f(int[] arr, int L, int R) {
+		if (L == R) {
+			return arr[L];
+		}
+		return Math.max(arr[L] + s(arr, L + 1, R), arr[R] + s(arr, L, R - 1));
+	}
+
+	public static int s(int[] arr, int L, int R) {
+		if (L == R) {
+			return 0;
+		}
+		return Math.min(f(arr, L + 1, R), f(arr, L, R - 1));
+	}
+
+	public static int windp(int[] arr) {
+		if (arr == null || arr.length == 0) {
+			return 0;
+		}
+		int N = arr.length;
+		int[][] f = new int[N][N];
+		int[][] s = new int[N][N];
+		for (int i = 0; i < N; i++) {
+			f[i][i] = arr[i];
+		}
+		// 0,0 右下方移动
+		// 0,1
+		// 0,2
+		// 0,N-1
+		for (int col = 1; col < N; col++) {
+			// 对角线出发位置(0,col)
+			int L = 0;
+			int R = col;
+			while (L < N && R < N) {
+				f[L][R] = Math.max(arr[L] + s[L + 1][R], arr[R] + s[L][R - 1]);
+				s[L][R] = Math.min(f[L + 1][R], f[L][R - 1]);
+				L++;
+				R++;
+			}
+		}
+		return Math.max(f[0][N - 1], s[0][N - 1]);
+	}
+
+	public static void main(String[] args) {
+		int[] arr = { 5, 7, 4, 5, 8, 1, 6, 0, 3, 4, 6, 1, 7 };
+		System.out.println(win1(arr));
+		System.out.println(windp(arr));
+
+	}
+
+}
diff --git a/src/class12/Code05_PalindromeSubsequence.java b/src/class12/Code05_PalindromeSubsequence.java
new file mode 100644
index 0000000..bb6f089
--- /dev/null
+++ b/src/class12/Code05_PalindromeSubsequence.java
@@ -0,0 +1,29 @@
+package class12;
+
+public class Code05_PalindromeSubsequence {
+
+	public static int lcse(char[] str1, char[] str2) {
+		int[][] dp = new int[str1.length][str2.length];
+		dp[0][0] = str1[0] == str2[0] ? 1 : 0;
+		for (int i = 1; i < str1.length; i++) {
+			dp[i][0] = Math.max(dp[i - 1][0], str1[i] == str2[0] ? 1 : 0);
+		}
+		for (int j = 1; j < str2.length; j++) {
+			dp[0][j] = Math.max(dp[0][j - 1], str1[0] == str2[j] ? 1 : 0);
+		}
+		for (int i = 1; i < str1.length; i++) {
+			for (int j = 1; j < str2.length; j++) {
+				dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
+				if (str1[i] == str2[j]) {
+					dp[i][j] = Math.max(dp[i][j], dp[i - 1][j - 1] + 1);
+				}
+			}
+		}
+		return dp[str1.length - 1][str2.length - 1];
+	}
+
+	public static void main(String[] args) {
+
+	}
+
+}
diff --git a/src/class12/Code06_Coffee.java b/src/class12/Code06_Coffee.java
new file mode 100644
index 0000000..99750b5
--- /dev/null
+++ b/src/class12/Code06_Coffee.java
@@ -0,0 +1,183 @@
+package class12;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.PriorityQueue;
+
+// 题目
+// 数组arr代表每一个咖啡机冲一杯咖啡的时间，每个咖啡机只能串行的制造咖啡。
+// 现在有n个人需要喝咖啡，只能用咖啡机来制造咖啡。
+// 认为每个人喝咖啡的时间非常短，冲好的时间即是喝完的时间。
+// 每个人喝完之后咖啡杯可以选择洗或者自然挥发干净，只有一台洗咖啡杯的机器，只能串行的洗咖啡杯。
+// 洗杯子的机器洗完一个杯子时间为a，任何一个杯子自然挥发干净的时间为b。
+// 四个参数：arr, n, a, b
+// 假设时间点从0开始，返回所有人喝完咖啡并洗完咖啡杯的全部过程结束后，至少来到什么时间点。
+public class Code06_Coffee {
+
+	// 方法一：暴力尝试方法
+	public static int minTime1(int[] arr, int n, int a, int b) {
+		int[] times = new int[arr.length];
+		int[] drink = new int[n];
+		return forceMake(arr, times, 0, drink, n, a, b);
+	}
+
+	// 方法一，每个人暴力尝试用每一个咖啡机给自己做咖啡
+	public static int forceMake(int[] arr, int[] times, int kth, int[] drink, int n, int a, int b) {
+		if (kth == n) {
+			int[] drinkSorted = Arrays.copyOf(drink, kth);
+			Arrays.sort(drinkSorted);
+			return forceWash(drinkSorted, a, b, 0, 0, 0);
+		}
+		int time = Integer.MAX_VALUE;
+		for (int i = 0; i < arr.length; i++) {
+			int work = arr[i];
+			int pre = times[i];
+			drink[kth] = pre + work;
+			times[i] = pre + work;
+			time = Math.min(time, forceMake(arr, times, kth + 1, drink, n, a, b));
+			drink[kth] = 0;
+			times[i] = pre;
+		}
+		return time;
+	}
+
+	// 方法一，暴力尝试洗咖啡杯的方式
+	public static int forceWash(int[] drinks, int a, int b, int index, int washLine, int time) {
+		if (index == drinks.length) {
+			return time;
+		}
+		// 选择一：当前index号咖啡杯，选择用洗咖啡机刷干净
+		int wash = Math.max(drinks[index], washLine) + a;
+		int ans1 = forceWash(drinks, a, b, index + 1, wash, Math.max(wash, time));
+
+		// 选择二：当前index号咖啡杯，选择自然挥发
+		int dry = drinks[index] + b;
+		int ans2 = forceWash(drinks, a, b, index + 1, washLine, Math.max(dry, time));
+		return Math.min(ans1, ans2);
+	}
+
+	// 方法二：稍微好一点的解法
+	public static class Machine {
+		public int timePoint;
+		public int workTime;
+
+		public Machine(int t, int w) {
+			timePoint = t;
+			workTime = w;
+		}
+	}
+
+	public static class MachineComparator implements Comparator<Machine> {
+
+		@Override
+		public int compare(Machine o1, Machine o2) {
+			return (o1.timePoint + o1.workTime) - (o2.timePoint + o2.workTime);
+		}
+
+	}
+
+	// 方法二，每个人暴力尝试用每一个咖啡机给自己做咖啡，优化成贪心
+	public static int minTime2(int[] arr, int n, int a, int b) {
+		PriorityQueue<Machine> heap = new PriorityQueue<Machine>(new MachineComparator());
+		for (int i = 0; i < arr.length; i++) {
+			heap.add(new Machine(0, arr[i]));
+		}
+		int[] drinks = new int[n];
+		for (int i = 0; i < n; i++) {
+			Machine cur = heap.poll();
+			cur.timePoint += cur.workTime;
+			drinks[i] = cur.timePoint;
+			heap.add(cur);
+		}
+		return process(drinks, a, b, 0, 0);
+	}
+
+	// 方法二，洗咖啡杯的方式和原来一样，只是这个暴力版本减少了一个可变参数
+	public static int process(int[] drinks, int a, int b, int index, int washLine) {
+		if (index == drinks.length - 1) {
+			return Math.min(Math.max(washLine, drinks[index]) + a, drinks[index] + b);
+		}
+		// wash是我当前的咖啡杯，洗完的时间
+		int wash = Math.max(washLine, drinks[index]) + a;
+		int next1 = process(drinks, a, b, index + 1, wash);
+		int p1 = Math.max(wash, next1);
+		int dry = drinks[index] + b;
+		int next2 = process(drinks, a, b, index + 1, washLine);
+		int p2 = Math.max(dry, next2);
+		return Math.min(p1, p2);
+	}
+
+	// 方法三：最终版本，把方法二洗咖啡杯的暴力尝试进一步优化成动态规划
+	public static int minTime3(int[] arr, int n, int a, int b) {
+		PriorityQueue<Machine> heap = new PriorityQueue<Machine>(new MachineComparator());
+		for (int i = 0; i < arr.length; i++) {
+			heap.add(new Machine(0, arr[i]));
+		}
+		int[] drinks = new int[n];
+		for (int i = 0; i < n; i++) {
+			Machine cur = heap.poll();
+			cur.timePoint += cur.workTime;
+			drinks[i] = cur.timePoint;
+			heap.add(cur);
+		}
+		if (a >= b) {
+			return drinks[n - 1] + b;
+		}
+		int[][] dp = new int[n][drinks[n - 1] + n * a];
+		for (int i = 0; i < dp[0].length; i++) {
+			dp[n - 1][i] = Math.min(Math.max(i, drinks[n - 1]) + a, drinks[n - 1] + b);
+		}
+		for (int row = n - 2; row >= 0; row--) { // row 咖啡杯的编号
+			int washLine = drinks[row] + (row + 1) * a;
+			for (int col = 0; col < washLine; col++) {
+				int wash = Math.max(col, drinks[row]) + a;
+				dp[row][col] = Math.min(Math.max(wash, dp[row + 1][wash]), Math.max(drinks[row] + b, dp[row + 1][col]));
+			}
+		}
+		return dp[0][0];
+	}
+
+	// for test
+	public static int[] randomArray(int len, int max) {
+		int[] arr = new int[len];
+		for (int i = 0; i < len; i++) {
+			arr[i] = (int) (Math.random() * max) + 1;
+		}
+		return arr;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		System.out.print("arr : ");
+		for (int j = 0; j < arr.length; j++) {
+			System.out.print(arr[j] + ", ");
+		}
+		System.out.println();
+	}
+
+	public static void main(String[] args) {
+		int len = 5;
+		int max = 9;
+		int testTime = 50000;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr = randomArray(len, max);
+			int n = (int) (Math.random() * 5) + 1;
+			int a = (int) (Math.random() * 5) + 1;
+			int b = (int) (Math.random() * 10) + 1;
+			int ans1 = minTime1(arr, n, a, b);
+			int ans2 = minTime2(arr, n, a, b);
+			int ans3 = minTime3(arr, n, a, b);
+			if (ans1 != ans2 || ans2 != ans3) {
+				printArray(arr);
+				System.out.println("n : " + n);
+				System.out.println("a : " + a);
+				System.out.println("b : " + b);
+				System.out.println(ans1 + " , " + ans2 + " , " + ans3);
+				System.out.println("===============");
+				break;
+			}
+		}
+
+	}
+
+}
diff --git a/src/class12/Code07_HorseJump.java b/src/class12/Code07_HorseJump.java
new file mode 100644
index 0000000..2d2ab17
--- /dev/null
+++ b/src/class12/Code07_HorseJump.java
@@ -0,0 +1,69 @@
+package class12;
+
+public class Code07_HorseJump {
+
+	// 10*9
+	// 0~9 y
+	// 0~8 x
+	public static int ways(int a, int b, int step) {
+		return f(0, 0, step, a, b);
+	}
+
+	// 马在(i,j)位置，还有step步要去跳
+	// 返回最终来到(a,b)的方法数
+	public static int f(int i, int j, int step, int a, int b) {
+		if (i < 0 || i > 9 || j < 0 || j > 8) {
+			return 0;
+		}
+		if (step == 0) {
+			return (i == a && j == b) ? 1 : 0;
+		}
+		return f(i - 2, j + 1, step - 1, a, b) 
+				+ f(i - 1, j + 2, step - 1, a, b) 
+				+ f(i + 1, j + 2, step - 1, a, b)
+				+ f(i + 2, j + 1, step - 1, a, b) 
+				+ f(i + 2, j - 1, step - 1, a, b) 
+				+ f(i + 1, j - 2, step - 1, a, b)
+				+ f(i - 1, j - 2, step - 1, a, b) 
+				+ f(i - 2, j - 1, step - 1, a, b);
+
+	}
+	
+	
+	public static int waysdp(int a, int b, int s) {
+		// (i,j,0~ step)
+		int[][][] dp = new int[10][9][s+1];
+		dp[a][b][0] = 1;
+		for(int step = 1 ; step <= s;step++ ) { // 按层来
+			for(int i = 0 ; i < 10;i++) {
+				for(int j = 0 ; j < 9; j++) {
+					dp[i][j][step] = getValue(dp,i - 2, j + 1, step - 1) 
+							+ getValue(dp,i - 1, j + 2, step - 1) 
+							+ getValue(dp,i + 1, j + 2, step - 1)
+							+ getValue(dp,i + 2, j + 1, step - 1) 
+							+ getValue(dp,i + 2, j - 1, step - 1) 
+							+ getValue(dp,i + 1, j - 2, step - 1)
+							+ getValue(dp,i - 1, j - 2, step - 1) 
+							+ getValue(dp,i - 2, j - 1, step - 1);
+				}
+			}
+		}
+		return dp[0][0][s];
+	}
+
+	// 在dp表中，得到dp[i][j][step]的值，但如果(i，j)位置越界的话，返回0；
+	public static int getValue(int[][][] dp, int i, int j, int step) {
+		if (i < 0 || i > 9 || j < 0 || j > 8) {
+			return 0;
+		}
+		return dp[i][j][step];
+	}
+
+	public static void main(String[] args) {
+		int x = 7;
+		int y = 7;
+		int step = 10;
+		System.out.println(ways(x, y, step));
+		System.out.println(waysdp(x, y, step));
+	}
+}
diff --git a/src/class12/Code08_MinPathSum.java b/src/class12/Code08_MinPathSum.java
new file mode 100644
index 0000000..9aae0a3
--- /dev/null
+++ b/src/class12/Code08_MinPathSum.java
@@ -0,0 +1,82 @@
+package class12;
+
+public class Code08_MinPathSum {
+
+	public static int minPathSum1(int[][] m) {
+		if (m == null || m.length == 0 || m[0] == null || m[0].length == 0) {
+			return 0;
+		}
+		int row = m.length;
+		int col = m[0].length;
+		int[][] dp = new int[row][col];
+		dp[0][0] = m[0][0];
+		for (int i = 1; i < row; i++) {
+			dp[i][0] = dp[i - 1][0] + m[i][0];
+		}
+		for (int j = 1; j < col; j++) {
+			dp[0][j] = dp[0][j - 1] + m[0][j];
+		}
+		for (int i = 1; i < row; i++) {
+			for (int j = 1; j < col; j++) {
+				dp[i][j] = Math.min(dp[i - 1][j], dp[i][j - 1]) + m[i][j];
+			}
+		}
+		return dp[row - 1][col - 1];
+	}
+
+	public static int minPathSum2(int[][] m) {
+		if (m == null || m.length == 0 || m[0] == null || m[0].length == 0) {
+			return 0;
+		}
+		int more = Math.max(m.length, m[0].length); // �����������ϴ���Ǹ�Ϊmore
+		int less = Math.min(m.length, m[0].length); // ������������С���Ǹ�Ϊless
+		boolean rowmore = more == m.length; // �����Dz��Ǵ��ڵ�������
+		int[] arr = new int[less]; // ��������ij��Ƚ�Ϊ�����������е���Сֵ
+		arr[0] = m[0][0];
+		for (int i = 1; i < less; i++) {
+			arr[i] = arr[i - 1] + (rowmore ? m[0][i] : m[i][0]);
+		}
+		for (int i = 1; i < more; i++) {
+			arr[0] = arr[0] + (rowmore ? m[i][0] : m[0][i]);
+			for (int j = 1; j < less; j++) {
+				arr[j] = Math.min(arr[j - 1], arr[j])
+						+ (rowmore ? m[i][j] : m[j][i]);
+			}
+		}
+		return arr[less - 1];
+	}
+
+	// for test
+	public static int[][] generateRandomMatrix(int rowSize, int colSize) {
+		if (rowSize < 0 || colSize < 0) {
+			return null;
+		}
+		int[][] result = new int[rowSize][colSize];
+		for (int i = 0; i != result.length; i++) {
+			for (int j = 0; j != result[0].length; j++) {
+				result[i][j] = (int) (Math.random() * 10);
+			}
+		}
+		return result;
+	}
+
+	// for test
+	public static void printMatrix(int[][] matrix) {
+		for (int i = 0; i != matrix.length; i++) {
+			for (int j = 0; j != matrix[0].length; j++) {
+				System.out.print(matrix[i][j] + " ");
+			}
+			System.out.println();
+		}
+	}
+
+	public static void main(String[] args) {
+		// int[][] m = generateRandomMatrix(3, 4);
+		int[][] m = { { 1, 3, 5, 9 }, { 8, 1, 3, 4 }, { 5, 0, 6, 1 },
+				{ 8, 8, 4, 0 } };
+		printMatrix(m);
+		System.out.println(minPathSum1(m));
+		System.out.println(minPathSum2(m));
+
+	}
+}
diff --git a/src/class12/Code09_CoinsWay.java b/src/class12/Code09_CoinsWay.java
new file mode 100644
index 0000000..59fd827
--- /dev/null
+++ b/src/class12/Code09_CoinsWay.java
@@ -0,0 +1,52 @@
+package class12;
+
+public class Code09_CoinsWay {
+
+	// arr中都是正数且无重复值，返回组成aim的方法数
+	public static int ways(int[] arr, int aim) {
+		if (arr == null || arr.length == 0 || aim < 0) {
+			return 0;
+		}
+		return process(arr, 0, aim);
+	}
+
+	// 如果自由使用arr[index...]的面值，组成rest这么多钱，返回方法数 （1 , 6）
+	public static int process(int[] arr, int index, int rest) {
+		if (index == arr.length) { // 无面值的时候
+			return rest == 0 ? 1 : 0;
+		}
+		// 有面值的时候
+		int ways = 0;
+		// arr[index] 当钱面值
+		for (int zhang = 0; zhang * arr[index] <= rest; zhang++) {
+			ways += process(arr, index + 1, rest - zhang * arr[index]);
+		}
+		return ways;
+	}
+
+	public static int waysdp(int[] arr, int aim) {
+		if (arr == null || arr.length == 0 || aim < 0) {
+			return 0;
+		}
+		int N = arr.length;
+		int[][] dp = new int[N + 1][aim + 1];
+		dp[N][0] = 1;
+		for (int i = N - 1; i >= 0; i--) { // 大顺序 从下往上
+			for (int rest = 0; rest <= aim; rest++) {
+				dp[i][rest] = dp[i + 1][rest];
+				if (rest - arr[i] >= 0) {
+					dp[i][rest] += dp[i][rest - arr[i]];
+				}
+			}
+		}
+		return dp[0][aim];
+	}
+
+	public static void main(String[] args) {
+		int[] arr = { 5, 2, 3, 1 };
+		int sum = 350;
+		System.out.println(ways(arr, sum));
+		System.out.println(waysdp(arr, sum));
+	}
+
+}