diff --git a/MCA算法突击课/第02期/mca_01/Code03_IsCBT.java b/MCA算法突击课/第02期/mca_01/Code03_IsCBT.java
new file mode 100644
index 0000000..83a4811
--- /dev/null
+++ b/MCA算法突击课/第02期/mca_01/Code03_IsCBT.java
@@ -0,0 +1,120 @@
+package 第02期.mca_01;
+
+import java.util.LinkedList;
+
+// 测试链接 : https://leetcode.com/problems/check-completeness-of-a-binary-tree/
+
+public class Code03_IsCBT {
+
+	// 不要提交这个类
+	public static class TreeNode {
+		public int val;
+		public TreeNode left;
+		public TreeNode right;
+
+		public TreeNode(int v) {
+			val = v;
+		}
+	}
+
+	public static boolean isCompleteTree1(TreeNode head) {
+		if (head == null) {
+			return true;
+		}
+		LinkedList<TreeNode> queue = new LinkedList<>();
+		// 是否遇到过左右两个孩子不双全的节点
+		boolean leaf = false;
+		TreeNode l = null;
+		TreeNode 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 isCompleteTree2(TreeNode head) {
+		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(TreeNode x) {
+		if (x == null) {
+			return new Info(true, true, 0);
+		}
+		Info leftInfo = process(x.left);
+		Info rightInfo = process(x.right);
+		int height = Math.max(leftInfo.height, rightInfo.height) + 1;
+		boolean isFull = leftInfo.isFull && rightInfo.isFull && leftInfo.height == rightInfo.height;
+		boolean isCBT = false;
+		if (leftInfo.isFull && rightInfo.isFull && leftInfo.height == rightInfo.height) {
+			isCBT = true;
+		} else if (leftInfo.isCBT && rightInfo.isFull && leftInfo.height == rightInfo.height + 1) {
+			isCBT = true;
+		} else if (leftInfo.isFull && rightInfo.isFull && leftInfo.height == rightInfo.height + 1) {
+			isCBT = true;
+		} else if (leftInfo.isFull && rightInfo.isCBT && leftInfo.height == rightInfo.height) {
+			isCBT = true;
+		}
+		return new Info(isFull, isCBT, height);
+	}
+
+	// for test
+	public static TreeNode generateRandomBST(int maxLevel, int maxValue) {
+		return generate(1, maxLevel, maxValue);
+	}
+
+	// for test
+	public static TreeNode generate(int level, int maxLevel, int maxValue) {
+		if (level > maxLevel || Math.random() < 0.5) {
+			return null;
+		}
+		TreeNode head = new TreeNode((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++) {
+			TreeNode head = generateRandomBST(maxLevel, maxValue);
+			if (isCompleteTree1(head) != isCompleteTree2(head)) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("finish!");
+	}
+
+}
diff --git a/MCA算法突击课/第02期/mca_01/Code04_NumberOfIslands.java b/MCA算法突击课/第02期/mca_01/Code04_NumberOfIslands.java
new file mode 100644
index 0000000..a4be2b8
--- /dev/null
+++ b/MCA算法突击课/第02期/mca_01/Code04_NumberOfIslands.java
@@ -0,0 +1,317 @@
+package 第02期.mca_01;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Stack;
+
+// 本题为leetcode原题
+// 测试链接：https://leetcode.com/problems/number-of-islands/
+// 所有方法都可以直接通过
+public class Code04_NumberOfIslands {
+
+	public static int numIslands3(char[][] board) {
+		int islands = 0;
+		for (int i = 0; i < board.length; i++) {
+			for (int j = 0; j < board[0].length; j++) {
+				if (board[i][j] == '1') {
+					islands++;
+					infect(board, i, j);
+				}
+			}
+		}
+		return islands;
+	}
+
+	// 从(i,j)这个位置出发，把所有练成一片的'1'字符，变成0
+	public static void infect(char[][] board, int i, int j) {
+		if (i < 0 || i == board.length || j < 0 || j == board[0].length || board[i][j] != '1') {
+			return;
+		}
+		board[i][j] = 0;
+		infect(board, i - 1, j);
+		infect(board, i + 1, j);
+		infect(board, i, j - 1);
+		infect(board, i, j + 1);
+	}
+
+	public static int numIslands1(char[][] board) {
+		int row = board.length;
+		int col = board[0].length;
+		Dot[][] dots = new Dot[row][col];
+		List<Dot> dotList = new ArrayList<>();
+		for (int i = 0; i < row; i++) {
+			for (int j = 0; j < col; j++) {
+				if (board[i][j] == '1') {
+					dots[i][j] = new Dot();
+					dotList.add(dots[i][j]);
+				}
+			}
+		}
+		UnionFind1<Dot> uf = new UnionFind1<>(dotList);
+		for (int j = 1; j < col; j++) {
+			// (0,j)  (0,0)跳过了  (0,1) (0,2) (0,3)
+			if (board[0][j - 1] == '1' && board[0][j] == '1') {
+				uf.union(dots[0][j - 1], dots[0][j]);
+			}
+		}
+		for (int i = 1; i < row; i++) {
+			if (board[i - 1][0] == '1' && board[i][0] == '1') {
+				uf.union(dots[i - 1][0], dots[i][0]);
+			}
+		}
+		for (int i = 1; i < row; i++) {
+			for (int j = 1; j < col; j++) {
+				if (board[i][j] == '1') {
+					if (board[i][j - 1] == '1') {
+						uf.union(dots[i][j - 1], dots[i][j]);
+					}
+					if (board[i - 1][j] == '1') {
+						uf.union(dots[i - 1][j], dots[i][j]);
+					}
+				}
+			}
+		}
+		return uf.sets();
+	}
+
+	public static class Dot {
+
+	}
+
+	public static class Node<V> {
+
+		V value;
+
+		public Node(V v) {
+			value = v;
+		}
+
+	}
+
+	public static class UnionFind1<V> {
+		public HashMap<V, Node<V>> nodes;
+		public HashMap<Node<V>, Node<V>> parents;
+		public HashMap<Node<V>, Integer> sizeMap;
+
+		public UnionFind1(List<V> values) {
+			nodes = new HashMap<>();
+			parents = new HashMap<>();
+			sizeMap = new HashMap<>();
+			for (V cur : values) {
+				Node<V> node = new Node<>(cur);
+				nodes.put(cur, 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);
+			}
+			while (!path.isEmpty()) {
+				parents.put(path.pop(), cur);
+			}
+			return cur;
+		}
+
+		public void union(V a, V b) {
+			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);
+				Node<V> big = aSetSize >= bSetSize ? aHead : bHead;
+				Node<V> small = big == aHead ? bHead : aHead;
+				parents.put(small, big);
+				sizeMap.put(big, aSetSize + bSetSize);
+				sizeMap.remove(small);
+			}
+		}
+
+		public int sets() {
+			return sizeMap.size();
+		}
+
+	}
+
+	public static int numIslands2(char[][] board) {
+		int row = board.length;
+		int col = board[0].length;
+		UnionFind2 uf = new UnionFind2(board);
+		for (int j = 1; j < col; j++) {
+			if (board[0][j - 1] == '1' && board[0][j] == '1') {
+				uf.union(0, j - 1, 0, j);
+			}
+		}
+		for (int i = 1; i < row; i++) {
+			if (board[i - 1][0] == '1' && board[i][0] == '1') {
+				uf.union(i - 1, 0, i, 0);
+			}
+		}
+		for (int i = 1; i < row; i++) {
+			for (int j = 1; j < col; j++) {
+				if (board[i][j] == '1') {
+					if (board[i][j - 1] == '1') {
+						uf.union(i, j - 1, i, j);
+					}
+					if (board[i - 1][j] == '1') {
+						uf.union(i - 1, j, i, j);
+					}
+				}
+			}
+		}
+		return uf.sets();
+	}
+
+	public static class UnionFind2 {
+		private int[] parent;
+		private int[] size;
+		private int[] help;
+		private int col;
+		private int sets;
+
+		public UnionFind2(char[][] board) {
+			col = board[0].length;
+			sets = 0;
+			int row = board.length;
+			int len = row * col;
+			parent = new int[len];
+			size = new int[len];
+			help = new int[len];
+			for (int r = 0; r < row; r++) {
+				for (int c = 0; c < col; c++) {
+					if (board[r][c] == '1') {
+						int i = index(r, c);
+						parent[i] = i;
+						size[i] = 1;
+						sets++;
+					}
+				}
+			}
+		}
+
+		// (r,c) -> i
+		private int index(int r, int c) {
+			return r * col + c;
+		}
+
+		// 原始位置 -> 下标
+		private int find(int i) {
+			int hi = 0;
+			while (i != parent[i]) {
+				help[hi++] = i;
+				i = parent[i];
+			}
+			for (hi--; hi >= 0; hi--) {
+				parent[help[hi]] = i;
+			}
+			return i;
+		}
+
+		public void union(int r1, int c1, int r2, int c2) {
+			int i1 = index(r1, c1);
+			int i2 = index(r2, c2);
+			int f1 = find(i1);
+			int f2 = find(i2);
+			if (f1 != f2) {
+				if (size[f1] >= size[f2]) {
+					size[f1] += size[f2];
+					parent[f2] = f1;
+				} else {
+					size[f2] += size[f1];
+					parent[f1] = f2;
+				}
+				sets--;
+			}
+		}
+
+		public int sets() {
+			return sets;
+		}
+
+	}
+
+	// 为了测试
+	public static char[][] generateRandomMatrix(int row, int col) {
+		char[][] board = new char[row][col];
+		for (int i = 0; i < row; i++) {
+			for (int j = 0; j < col; j++) {
+				board[i][j] = Math.random() < 0.5 ? '1' : '0';
+			}
+		}
+		return board;
+	}
+
+	// 为了测试
+	public static char[][] copy(char[][] board) {
+		int row = board.length;
+		int col = board[0].length;
+		char[][] ans = new char[row][col];
+		for (int i = 0; i < row; i++) {
+			for (int j = 0; j < col; j++) {
+				ans[i][j] = board[i][j];
+			}
+		}
+		return ans;
+	}
+
+	// 为了测试
+	public static void main(String[] args) {
+		int row = 0;
+		int col = 0;
+		char[][] board1 = null;
+		char[][] board2 = null;
+		char[][] board3 = null;
+		long start = 0;
+		long end = 0;
+
+		row = 1000;
+		col = 1000;
+		board1 = generateRandomMatrix(row, col);
+		board2 = copy(board1);
+		board3 = copy(board1);
+
+		System.out.println("感染方法、并查集(map实现)、并查集(数组实现)的运行结果和运行时间");
+		System.out.println("随机生成的二维矩阵规模 : " + row + " * " + col);
+
+		start = System.currentTimeMillis();
+		System.out.println("感染方法的运行结果: " + numIslands3(board1));
+		end = System.currentTimeMillis();
+		System.out.println("感染方法的运行时间: " + (end - start) + " ms");
+
+		start = System.currentTimeMillis();
+		System.out.println("并查集(map实现)的运行结果: " + numIslands1(board2));
+		end = System.currentTimeMillis();
+		System.out.println("并查集(map实现)的运行时间: " + (end - start) + " ms");
+
+		start = System.currentTimeMillis();
+		System.out.println("并查集(数组实现)的运行结果: " + numIslands2(board3));
+		end = System.currentTimeMillis();
+		System.out.println("并查集(数组实现)的运行时间: " + (end - start) + " ms");
+
+		System.out.println();
+
+		row = 10000;
+		col = 10000;
+		board1 = generateRandomMatrix(row, col);
+		board3 = copy(board1);
+		System.out.println("感染方法、并查集(数组实现)的运行结果和运行时间");
+		System.out.println("随机生成的二维矩阵规模 : " + row + " * " + col);
+
+		start = System.currentTimeMillis();
+		System.out.println("感染方法的运行结果: " + numIslands3(board1));
+		end = System.currentTimeMillis();
+		System.out.println("感染方法的运行时间: " + (end - start) + " ms");
+
+		start = System.currentTimeMillis();
+		System.out.println("并查集(数组实现)的运行结果: " + numIslands2(board3));
+		end = System.currentTimeMillis();
+		System.out.println("并查集(数组实现)的运行时间: " + (end - start) + " ms");
+
+	}
+
+}
diff --git a/MCA算法突击课/第02期/mca_01/Problem01_WaterKing.java b/MCA算法突击课/第02期/mca_01/Problem01_WaterKing.java
new file mode 100644
index 0000000..a7a91f7
--- /dev/null
+++ b/MCA算法突击课/第02期/mca_01/Problem01_WaterKing.java
@@ -0,0 +1,32 @@
+package 第02期.mca_01;
+
+// 找到数组中的水王数
+// 本题来自，大厂刷题班，23节
+public class Problem01_WaterKing {
+
+	public static int waterKing(int[] arr) {
+		int cand = 0;
+		int hp = 0;
+		for (int i = 0; i < arr.length; i++) {
+			if (hp == 0) {
+				cand = arr[i];
+				hp = 1;
+			} else if (arr[i] == cand) {
+				hp++;
+			} else {
+				hp--;
+			}
+		}
+		if (hp == 0) {
+			return -1;
+		}
+		hp = 0;
+		for (int i = 0; i < arr.length; i++) {
+			if (arr[i] == cand) {
+				hp++;
+			}
+		}
+		return hp > arr.length / 2 ? cand : -1;
+	}
+
+}
diff --git a/MCA算法突击课/第02期/mca_01/Problem02_InsertDeleteGetRandom.java b/MCA算法突击课/第02期/mca_01/Problem02_InsertDeleteGetRandom.java
new file mode 100644
index 0000000..acb32c2
--- /dev/null
+++ b/MCA算法突击课/第02期/mca_01/Problem02_InsertDeleteGetRandom.java
@@ -0,0 +1,52 @@
+package 第02期.mca_01;
+
+import java.util.HashMap;
+
+// 测试链接 : https://leetcode.com/problems/insert-delete-getrandom-o1/
+public class Problem02_InsertDeleteGetRandom {
+
+	public class RandomizedSet {
+
+		private HashMap<Integer, Integer> keyIndexMap;
+		private HashMap<Integer, Integer> indexKeyMap;
+		private int size;
+
+		public RandomizedSet() {
+			keyIndexMap = new HashMap<Integer, Integer>();
+			indexKeyMap = new HashMap<Integer, Integer>();
+			size = 0;
+		}
+
+		public boolean insert(int val) {
+			if (!keyIndexMap.containsKey(val)) {
+				keyIndexMap.put(val, size);
+				indexKeyMap.put(size++, val);
+				return true;
+			}
+			return false;
+		}
+
+		public boolean remove(int val) {
+			if (keyIndexMap.containsKey(val)) {
+				int deleteIndex = keyIndexMap.get(val);
+				int lastIndex = --size;
+				int lastKey = indexKeyMap.get(lastIndex);
+				keyIndexMap.put(lastKey, deleteIndex);
+				indexKeyMap.put(deleteIndex, lastKey);
+				keyIndexMap.remove(val);
+				indexKeyMap.remove(lastIndex);
+				return true;
+			}
+			return false;
+		}
+
+		public int getRandom() {
+			if (size == 0) {
+				return -1;
+			}
+			int randomIndex = (int) (Math.random() * size);
+			return indexKeyMap.get(randomIndex);
+		}
+	}
+
+}
diff --git a/MCA算法突击课/第02期/mca_01/Problem03_LinkedListCycleII.java b/MCA算法突击课/第02期/mca_01/Problem03_LinkedListCycleII.java
new file mode 100644
index 0000000..3fb4963
--- /dev/null
+++ b/MCA算法突击课/第02期/mca_01/Problem03_LinkedListCycleII.java
@@ -0,0 +1,32 @@
+package 第02期.mca_01;
+
+public class Problem03_LinkedListCycleII {
+
+	// 这个类不用提交
+	public static class ListNode {
+		public int val;
+		public ListNode next;
+	}
+
+	public static ListNode detectCycle(ListNode head) {
+		if (head == null || head.next == null || head.next.next == null) {
+			return null;
+		}
+		ListNode slow = head.next;
+		ListNode fast = head.next.next;
+		while (slow != fast) {
+			if (fast.next == null || fast.next.next == null) {
+				return null;
+			}
+			fast = fast.next.next;
+			slow = slow.next;
+		}
+		fast = head;
+		while (slow != fast) {
+			slow = slow.next;
+			fast = fast.next;
+		}
+		return slow;
+	}
+
+}
diff --git a/MCA算法突击课/第02期/mca_01/Problem04_MinSwapStep.java b/MCA算法突击课/第02期/mca_01/Problem04_MinSwapStep.java
new file mode 100644
index 0000000..b3d46cd
--- /dev/null
+++ b/MCA算法突击课/第02期/mca_01/Problem04_MinSwapStep.java
@@ -0,0 +1,74 @@
+package 第02期.mca_01;
+
+public class Problem04_MinSwapStep {
+
+	// 一个数组中只有两种字符'G'和'B'，
+	// 可以让所有的G都放在左侧，所有的B都放在右侧
+    // 或者可以让所有的G都放在右侧，所有的B都放在左侧
+	// 但是只能在相邻字符之间进行交换操作，请问请问至少需要交换几次，
+	public static int minSteps1(String s) {
+		if (s == null || s.equals("")) {
+			return 0;
+		}
+		char[] str = s.toCharArray();
+		int step1 = 0;
+		int gi = 0;
+		for (int i = 0; i < str.length; i++) {
+			if (str[i] == 'G') {
+				step1 += i - (gi++);
+			}
+		}
+		int step2 = 0;
+		int bi = 0;
+		for (int i = 0; i < str.length; i++) {
+			if (str[i] == 'B') {
+				step2 += i - (bi++);
+			}
+		}
+		return Math.min(step1, step2);
+	}
+
+	// 可以让G在左，或者在右
+	public static int minSteps2(String s) {
+		if (s == null || s.equals("")) {
+			return 0;
+		}
+		char[] str = s.toCharArray();
+		int step1 = 0;
+		int step2 = 0;
+		int gi = 0;
+		int bi = 0;
+		for (int i = 0; i < str.length; i++) {
+			if (str[i] == 'G') { // 当前的G，去左边   方案1
+				step1 += i - (gi++);
+			} else {// 当前的B，去左边   方案2
+				step2 += i - (bi++);
+			}
+		}
+		return Math.min(step1, step2);
+	}
+
+	// 为了测试
+	public static String randomString(int maxLen) {
+		char[] str = new char[(int) (Math.random() * maxLen)];
+		for (int i = 0; i < str.length; i++) {
+			str[i] = Math.random() < 0.5 ? 'G' : 'B';
+		}
+		return String.valueOf(str);
+	}
+
+	public static void main(String[] args) {
+		int maxLen = 100;
+		int testTime = 1000000;
+		System.out.println("测试开始");
+		for (int i = 0; i < testTime; i++) {
+			String str = randomString(maxLen);
+			int ans1 = minSteps1(str);
+			int ans2 = minSteps2(str);
+			if (ans1 != ans2) {
+				System.out.println("Oops!");
+			}
+		}
+		System.out.println("测试结束");
+	}
+}
\ No newline at end of file
diff --git a/MCA算法突击课/第02期/即将开始/package-info.java b/MCA算法突击课/第02期/即将开始/package-info.java
deleted file mode 100644
index 546f5a8..0000000
--- a/MCA算法突击课/第02期/即将开始/package-info.java
+++ /dev/null
@@ -1 +0,0 @@
-package 第02期.即将开始;
\ No newline at end of file