diff --git a/src/class24/Code01_SlidingWindowMaxArray.java b/src/class24/Code01_SlidingWindowMaxArray.java
new file mode 100644
index 0000000..23671dc
--- /dev/null
+++ b/src/class24/Code01_SlidingWindowMaxArray.java
@@ -0,0 +1,103 @@
+package class24;
+
+import java.util.LinkedList;
+
+public class Code01_SlidingWindowMaxArray {
+
+	public static int[] getMaxWindow(int[] arr, int w) {
+		if (arr == null || w < 1 || arr.length < w) {
+			return null;
+		}
+		// 其中放的是位置，头代表 （大->小）尾
+		LinkedList<Integer> qmax = new LinkedList<Integer>();
+		int[] res = new int[arr.length - w + 1];
+		int index = 0;
+		// L...R
+		//     i
+		for (int R = 0; R < arr.length; R++) { // 当前让 i -> [i] 进窗口 ， i 就是 r
+			// R -> 值  可以放在比他大的数后，或者空
+			while (!qmax.isEmpty() && arr[qmax.peekLast()] <= arr[R]) {
+				qmax.pollLast();
+			}
+			qmax.addLast(R);
+			// 数进来了
+			// 如果窗口没有形成W的长度之前，不弹出数字的
+			if (qmax.peekFirst() == R - w) {
+				qmax.pollFirst();
+			}
+			// 以上窗口更新做完了
+			if (R >= w - 1) {
+				res[index++] = arr[qmax.peekFirst()];
+			}
+		}
+		return res;
+	}
+
+	// for test
+	public static int[] rightWay(int[] arr, int w) {
+		if (arr == null || w < 1 || arr.length < w) {
+			return null;
+		}
+		int[] res = new int[arr.length - w + 1];
+		int index = 0;
+		int L = 0;
+		int R = w - 1;
+		while (R < arr.length) {
+			int max = arr[L];
+			for (int i = L + 1; i <= R; i++) {
+				max = Math.max(max, arr[i]);
+
+			}
+			res[index++] = max;
+			L++;
+			R++;
+		}
+		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) (Math.random() * (maxValue + 1));
+		}
+		return arr;
+	}
+
+	// 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;
+	}
+
+	public static void main(String[] args) {
+		int testTime = 100000;
+		int maxSize = 100;
+		int maxValue = 100;
+		System.out.println("test begin");
+		for (int i = 0; i < testTime; i++) {
+			int[] arr = generateRandomArray(maxSize, maxValue);
+			int w = (int) (Math.random() * (arr.length + 1));
+			int[] ans1 = getMaxWindow(arr, w);
+			int[] ans2 = rightWay(arr, w);
+			if (!isEqual(ans1, ans2)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("test finish");
+	}
+
+}
diff --git a/src/class24/Code02_AllLessNumSubArray.java b/src/class24/Code02_AllLessNumSubArray.java
new file mode 100644
index 0000000..40f6107
--- /dev/null
+++ b/src/class24/Code02_AllLessNumSubArray.java
@@ -0,0 +1,85 @@
+package class24;
+
+import java.util.LinkedList;
+
+public class Code02_AllLessNumSubArray {
+
+	public static int getNum(int[] arr, int num) {
+		if (arr == null || arr.length == 0) {
+			return 0;
+		}
+		LinkedList<Integer> qmin = new LinkedList<Integer>();
+		LinkedList<Integer> qmax = new LinkedList<Integer>();
+		int L = 0;
+		int R = 0;
+		// [L..R) -> [0,0) 窗口内无数 [1,1)
+		// [0,1) -> [0~0]
+		int res = 0;
+		while (L < arr.length) { // L是开头位置，尝试每一个开头
+
+			// 如果此时窗口的开头是L,下面的while工作:R向右扩到违规为止
+
+			while (R < arr.length) { // R是最后一个达标位置的再下一个
+				while (!qmin.isEmpty() && arr[qmin.peekLast()] >= arr[R]) {
+					qmin.pollLast();
+				}
+				qmin.addLast(R);
+				// R -> arr[R],
+				while (!qmax.isEmpty() && arr[qmax.peekLast()] <= arr[R]) {
+					qmax.pollLast();
+				}
+				qmax.addLast(R);
+
+				if (arr[qmax.getFirst()] - arr[qmin.getFirst()] > num) {
+					break;
+				}
+				R++;
+			}
+
+			// R是最后一个达标位置的再下一个，第一个违规的位置
+			res += R - L;
+
+			if (qmin.peekFirst() == L) {
+				qmin.pollFirst();
+			}
+			if (qmax.peekFirst() == L) {
+				qmax.pollFirst();
+			}
+
+			L++;
+
+		}
+		return res;
+	}
+
+	// for test
+	public static int[] getRandomArray(int len) {
+		if (len < 0) {
+			return null;
+		}
+		int[] arr = new int[len];
+		for (int i = 0; i < len; i++) {
+			arr[i] = (int) (Math.random() * 10);
+		}
+		return arr;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		if (arr != null) {
+			for (int i = 0; i < arr.length; i++) {
+				System.out.print(arr[i] + " ");
+			}
+			System.out.println();
+		}
+	}
+
+	public static void main(String[] args) {
+		int[] arr = getRandomArray(30);
+		int num = 5;
+		printArray(arr);
+		System.out.println(getNum(arr, num));
+
+	}
+
+}
diff --git a/src/class24/Code03_GasStation.java b/src/class24/Code03_GasStation.java
new file mode 100644
index 0000000..b80906f
--- /dev/null
+++ b/src/class24/Code03_GasStation.java
@@ -0,0 +1,53 @@
+package class24;
+
+import java.util.LinkedList;
+
+// 测试链接：https://leetcode.com/problems/gas-station
+public class Code03_GasStation {
+
+	// 这个方法的时间复杂度O(N)，额外空间复杂度O(N)
+	public static int canCompleteCircuit(int[] gas, int[] cost) {
+		boolean[] good = goodArray(gas, cost);
+		for (int i = 0; i < gas.length; i++) {
+			if (good[i]) {
+				return i;
+			}
+		}
+		return -1;
+	}
+
+	public static boolean[] goodArray(int[] g, int[] c) {
+		int N = g.length;
+		int M = N << 1;
+		int[] arr = new int[M];
+		for (int i = 0; i < N; i++) {
+			arr[i] = g[i] - c[i];
+			arr[i + N] = g[i] - c[i];
+		}
+		for (int i = 1; i < M; i++) {
+			arr[i] += arr[i - 1];
+		}
+		LinkedList<Integer> w = new LinkedList<>();
+		for (int i = 0; i < N; i++) {
+			while (!w.isEmpty() && arr[w.peekLast()] >= arr[i]) {
+				w.pollLast();
+			}
+			w.addLast(i);
+		}
+		boolean[] ans = new boolean[N];
+		for (int offset = 0, i = 0, j = N; j < M; offset = arr[i++], j++) {
+			if (arr[w.peekFirst()] - offset >= 0) {
+				ans[i] = true;
+			}
+			if (w.peekFirst() == i) {
+				w.pollFirst();
+			}
+			while (!w.isEmpty() && arr[w.peekLast()] >= arr[j]) {
+				w.pollLast();
+			}
+			w.addLast(j);
+		}
+		return ans;
+	}
+
+}
diff --git a/src/class23/Code04_MinCoinsOnePaper.java b/src/class24/Code04_MinCoinsOnePaper.java
similarity index 99%
rename from src/class23/Code04_MinCoinsOnePaper.java
rename to src/class24/Code04_MinCoinsOnePaper.java
index bf48243..a0a73b8 100644
--- a/src/class23/Code04_MinCoinsOnePaper.java
+++ b/src/class24/Code04_MinCoinsOnePaper.java
@@ -1,4 +1,4 @@
-package class23;
+package class24;
 
 import java.util.HashMap;
 import java.util.Map.Entry;
diff --git a/src/class25/Code01_MonotonousStack.java b/src/class25/Code01_MonotonousStack.java
new file mode 100644
index 0000000..c9bb357
--- /dev/null
+++ b/src/class25/Code01_MonotonousStack.java
@@ -0,0 +1,158 @@
+package class25;
+
+import java.util.List;
+import java.util.ArrayList;
+import java.util.Stack;
+
+public class Code01_MonotonousStack {
+
+	public static int[][] getNearLessNoRepeat(int[] arr) {
+		int[][] res = new int[arr.length][2];
+		Stack<Integer> stack = new Stack<>();
+		for (int i = 0; i < arr.length; i++) {
+			while (!stack.isEmpty() && arr[stack.peek()] > arr[i]) {
+				int popIndex = stack.pop();
+				int leftLessIndex = stack.isEmpty() ? -1 : stack.peek();
+				res[popIndex][0] = leftLessIndex;
+				res[popIndex][1] = i;
+			}
+			stack.push(i);
+		}
+		while (!stack.isEmpty()) {
+			int popIndex = stack.pop();
+			int leftLessIndex = stack.isEmpty() ? -1 : stack.peek();
+			res[popIndex][0] = leftLessIndex;
+			res[popIndex][1] = -1;
+		}
+		return res;
+	}
+
+	public static int[][] getNearLess(int[] arr) {
+		int[][] res = new int[arr.length][2];
+		Stack<List<Integer>> stack = new Stack<>();
+		for (int i = 0; i < arr.length; i++) { // i -> arr[i] 进栈
+			// 底 -> 顶， 小 -> 大
+			while (!stack.isEmpty() && arr[stack.peek().get(0)] > arr[i]) {
+				List<Integer> popIs = stack.pop();
+				// 取位于下面位置的列表中，最晚加入的那个
+				int leftLessIndex = stack.isEmpty() ? -1 : stack.peek().get(stack.peek().size() - 1);
+				for (Integer popi : popIs) {
+					res[popi][0] = leftLessIndex;
+					res[popi][1] = i;
+				}
+			}
+			// 相等的、比你小的
+			if (!stack.isEmpty() && arr[stack.peek().get(0)] == arr[i]) {
+				stack.peek().add(Integer.valueOf(i));
+			} else {
+				ArrayList<Integer> list = new ArrayList<>();
+				list.add(i);
+				stack.push(list);
+			}
+		}
+		while (!stack.isEmpty()) {
+			List<Integer> popIs = stack.pop();
+			// 取位于下面位置的列表中，最晚加入的那个
+			int leftLessIndex = stack.isEmpty() ? -1 : stack.peek().get(stack.peek().size() - 1);
+			for (Integer popi : popIs) {
+				res[popi][0] = leftLessIndex;
+				res[popi][1] = -1;
+			}
+		}
+		return res;
+	}
+
+	// for test
+	public static int[] getRandomArrayNoRepeat(int size) {
+		int[] arr = new int[(int) (Math.random() * size) + 1];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = i;
+		}
+		for (int i = 0; i < arr.length; i++) {
+			int swapIndex = (int) (Math.random() * arr.length);
+			int tmp = arr[swapIndex];
+			arr[swapIndex] = arr[i];
+			arr[i] = tmp;
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[] getRandomArray(int size, int max) {
+		int[] arr = new int[(int) (Math.random() * size) + 1];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) (Math.random() * max) - (int) (Math.random() * max);
+		}
+		return arr;
+	}
+
+	// for test
+	public static int[][] rightWay(int[] arr) {
+		int[][] res = new int[arr.length][2];
+		for (int i = 0; i < arr.length; i++) {
+			int leftLessIndex = -1;
+			int rightLessIndex = -1;
+			int cur = i - 1;
+			while (cur >= 0) {
+				if (arr[cur] < arr[i]) {
+					leftLessIndex = cur;
+					break;
+				}
+				cur--;
+			}
+			cur = i + 1;
+			while (cur < arr.length) {
+				if (arr[cur] < arr[i]) {
+					rightLessIndex = cur;
+					break;
+				}
+				cur++;
+			}
+			res[i][0] = leftLessIndex;
+			res[i][1] = rightLessIndex;
+		}
+		return res;
+	}
+
+	// for test
+	public static boolean isEqual(int[][] res1, int[][] res2) {
+		if (res1.length != res2.length) {
+			return false;
+		}
+		for (int i = 0; i < res1.length; i++) {
+			if (res1[i][0] != res2[i][0] || res1[i][1] != res2[i][1]) {
+				return false;
+			}
+		}
+
+		return true;
+	}
+
+	// for test
+	public static void printArray(int[] arr) {
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	public static void main(String[] args) {
+		int size = 10;
+		int max = 20;
+		int testTimes = 2000000;
+		for (int i = 0; i < testTimes; i++) {
+			int[] arr1 = getRandomArrayNoRepeat(size);
+			int[] arr2 = getRandomArray(size, max);
+			if (!isEqual(getNearLessNoRepeat(arr1), rightWay(arr1))) {
+				System.out.println("Oops!");
+				printArray(arr1);
+				break;
+			}
+			if (!isEqual(getNearLess(arr2), rightWay(arr2))) {
+				System.out.println("Oops!");
+				printArray(arr2);
+				break;
+			}
+		}
+	}
+}
diff --git a/src/class25/Code02_AllTimesMinToMax.java b/src/class25/Code02_AllTimesMinToMax.java
new file mode 100644
index 0000000..d0cdef8
--- /dev/null
+++ b/src/class25/Code02_AllTimesMinToMax.java
@@ -0,0 +1,67 @@
+package class25;
+
+import java.util.Stack;
+
+public class Code02_AllTimesMinToMax {
+
+	public static int max1(int[] arr) {
+		int max = Integer.MIN_VALUE;
+		for (int i = 0; i < arr.length; i++) {
+			for (int j = i; j < arr.length; j++) {
+				int minNum = Integer.MAX_VALUE;
+				int sum = 0;
+				for (int k = i; k <= j; k++) {
+					sum += arr[k];
+					minNum = Math.min(minNum, arr[k]);
+				}
+				max = Math.max(max, minNum * sum);
+			}
+		}
+		return max;
+	}
+
+	public static int max2(int[] arr) {
+		int size = arr.length;
+		int[] sums = new int[size];
+		sums[0] = arr[0];
+		for (int i = 1; i < size; i++) {
+			sums[i] = sums[i - 1] + arr[i];
+		}
+		int max = Integer.MIN_VALUE;
+		Stack<Integer> stack = new Stack<Integer>();
+		for (int i = 0; i < size; i++) {
+			while (!stack.isEmpty() && arr[stack.peek()] >= arr[i]) {
+				int j = stack.pop();
+				max = Math.max(max, (stack.isEmpty() ? sums[i - 1] : (sums[i - 1] - sums[stack.peek()])) * arr[j]);
+			}
+			stack.push(i);
+		}
+		while (!stack.isEmpty()) {
+			int j = stack.pop();
+			max = Math.max(max, (stack.isEmpty() ? sums[size - 1] : (sums[size - 1] - sums[stack.peek()])) * arr[j]);
+		}
+		return max;
+	}
+
+	public static int[] gerenareRondomArray() {
+		int[] arr = new int[(int) (Math.random() * 20) + 10];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) (Math.random() * 101);
+		}
+		return arr;
+	}
+
+	public static void main(String[] args) {
+		int testTimes = 2000000;
+		System.out.println("test begin");
+		for (int i = 0; i < testTimes; i++) {
+			int[] arr = gerenareRondomArray();
+			if (max1(arr) != max2(arr)) {
+				System.out.println("FUCK!");
+				break;
+			}
+		}
+		System.out.println("test finish");
+	}
+
+}
diff --git a/src/class25/Code03_SumOfSubarrayMinimums.java b/src/class25/Code03_SumOfSubarrayMinimums.java
new file mode 100644
index 0000000..12e4741
--- /dev/null
+++ b/src/class25/Code03_SumOfSubarrayMinimums.java
@@ -0,0 +1,153 @@
+package class25;
+
+import java.util.Stack;
+
+// 测试链接：https://leetcode.com/problems/sum-of-subarray-minimums/
+// subArrayMinSum1是暴力解
+// subArrayMinSum2是最优解的思路
+// sumSubarrayMins是最优解思路下的单调栈优化
+// Leetcode上只提交sumSubarrayMins方法，时间复杂度O(N)，可以直接通过
+public class Code03_SumOfSubarrayMinimums {
+
+	public static int subArrayMinSum1(int[] arr) {
+		int ans = 0;
+		for (int i = 0; i < arr.length; i++) {
+			for (int j = i; j < arr.length; j++) {
+				int min = arr[i];
+				for (int k = i + 1; k <= j; k++) {
+					min = Math.min(min, arr[k]);
+				}
+				ans += min;
+			}
+		}
+		return ans;
+	}
+
+	public static int subArrayMinSum2(int[] arr) {
+		int[] left = leftNearLessEqual2(arr);
+		int[] right = rightNearLess2(arr);
+		int ans = 0;
+		for (int i = 0; i < arr.length; i++) {
+			int start = i - left[i];
+			int end = right[i] - i;
+			ans += start * end * arr[i];
+		}
+		return ans;
+	}
+
+	public static int[] leftNearLessEqual2(int[] arr) {
+		int N = arr.length;
+		int[] left = new int[N];
+		for (int i = 0; i < N; i++) {
+			int ans = -1;
+			for (int j = i - 1; j >= 0; j--) {
+				if (arr[j] <= arr[i]) {
+					ans = j;
+					break;
+				}
+			}
+			left[i] = ans;
+		}
+		return left;
+	}
+
+	public static int[] rightNearLess2(int[] arr) {
+		int N = arr.length;
+		int[] right = new int[N];
+		for (int i = 0; i < N; i++) {
+			int ans = N;
+			for (int j = i + 1; j < N; j++) {
+				if (arr[i] > arr[j]) {
+					ans = j;
+					break;
+				}
+			}
+			right[i] = ans;
+		}
+		return right;
+	}
+
+	public static int sumSubarrayMins(int[] arr) {
+		int[] left = nearLessEqualLeft(arr);
+		int[] right = nearLessRight(arr);
+		long ans = 0;
+		for (int i = 0; i < arr.length; i++) {
+			long start = i - left[i];
+			long end = right[i] - i;
+			ans += start * end * (long) arr[i];
+			ans %= 1000000007;
+		}
+		return (int) ans;
+	}
+
+	public static int[] nearLessEqualLeft(int[] arr) {
+		int N = arr.length;
+		int[] left = new int[N];
+		Stack<Integer> stack = new Stack<>();
+		for (int i = N - 1; i >= 0; i--) {
+			while (!stack.isEmpty() && arr[i] <= arr[stack.peek()]) {
+				left[stack.pop()] = i;
+			}
+			stack.push(i);
+		}
+		while (!stack.isEmpty()) {
+			left[stack.pop()] = -1;
+		}
+		return left;
+	}
+
+	public static int[] nearLessRight(int[] arr) {
+		int N = arr.length;
+		int[] right = new int[N];
+		Stack<Integer> stack = new Stack<>();
+		for (int i = 0; i < N; i++) {
+			while (!stack.isEmpty() && arr[stack.peek()] > arr[i]) {
+				right[stack.pop()] = i;
+			}
+			stack.push(i);
+		}
+		while (!stack.isEmpty()) {
+			right[stack.pop()] = N;
+		}
+		return right;
+	}
+
+	public static int[] randomArray(int len, int maxValue) {
+		int[] ans = new int[len];
+		for (int i = 0; i < len; i++) {
+			ans[i] = (int) (Math.random() * maxValue) + 1;
+		}
+		return ans;
+	}
+
+	public static void printArray(int[] arr) {
+		for (int i = 0; i < arr.length; i++) {
+			System.out.print(arr[i] + " ");
+		}
+		System.out.println();
+	}
+
+	public static void main(String[] args) {
+		int maxLen = 100;
+		int maxValue = 50;
+		int testTime = 100000;
+		System.out.println("测试开始");
+		for (int i = 0; i < testTime; i++) {
+			int len = (int) (Math.random() * maxLen);
+			int[] arr = randomArray(len, maxValue);
+			int ans1 = subArrayMinSum1(arr);
+			int ans2 = subArrayMinSum2(arr);
+			int ans3 = sumSubarrayMins(arr);
+			if (ans1 != ans2 || ans1 != ans3) {
+				printArray(arr);
+				System.out.println(ans1);
+				System.out.println(ans2);
+				System.out.println(ans3);
+				System.out.println("出错了！");
+				break;
+			}
+		}
+		System.out.println("测试结束");
+	}
+
+}
diff --git a/src/class25/Code04_LargestRectangleInHistogram.java b/src/class25/Code04_LargestRectangleInHistogram.java
new file mode 100644
index 0000000..1123ef7
--- /dev/null
+++ b/src/class25/Code04_LargestRectangleInHistogram.java
@@ -0,0 +1,58 @@
+package class25;
+
+import java.util.Stack;
+
+// 测试链接：https://leetcode.com/problems/largest-rectangle-in-histogram
+public class Code04_LargestRectangleInHistogram {
+
+	public static int largestRectangleArea1(int[] height) {
+		if (height == null || height.length == 0) {
+			return 0;
+		}
+		int maxArea = 0;
+		Stack<Integer> stack = new Stack<Integer>();
+		for (int i = 0; i < height.length; i++) {
+			while (!stack.isEmpty() && height[i] <= height[stack.peek()]) {
+				int j = stack.pop();
+				int k = stack.isEmpty() ? -1 : stack.peek();
+				int curArea = (i - k - 1) * height[j];
+				maxArea = Math.max(maxArea, curArea);
+			}
+			stack.push(i);
+		}
+		while (!stack.isEmpty()) {
+			int j = stack.pop();
+			int k = stack.isEmpty() ? -1 : stack.peek();
+			int curArea = (height.length - k - 1) * height[j];
+			maxArea = Math.max(maxArea, curArea);
+		}
+		return maxArea;
+	}
+
+	public static int largestRectangleArea2(int[] height) {
+		if (height == null || height.length == 0) {
+			return 0;
+		}
+		int N = height.length;
+		int[] stack = new int[N];
+		int si = -1;
+		int maxArea = 0;
+		for (int i = 0; i < height.length; i++) {
+			while (si != -1 && height[i] <= height[stack[si]]) {
+				int j = stack[si--];
+				int k = si == -1 ? -1 : stack[si];
+				int curArea = (i - k - 1) * height[j];
+				maxArea = Math.max(maxArea, curArea);
+			}
+			stack[++si] = i;
+		}
+		while (si != -1) {
+			int j = stack[si--];
+			int k = si == -1 ? -1 : stack[si];
+			int curArea = (height.length - k - 1) * height[j];
+			maxArea = Math.max(maxArea, curArea);
+		}
+		return maxArea;
+	}
+
+}