diff --git a/Week_01/id_38/LeetCode_104_038.java b/Week_01/id_38/LeetCode_104_038.java
new file mode 100644
index 00000000..13cde551
--- /dev/null
+++ b/Week_01/id_38/LeetCode_104_038.java
@@ -0,0 +1,40 @@
+/*
+ * @lc app=leetcode.cn id=104 lang=java
+ *
+ * [104] 二叉树的最大深度
+ */
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ * int val;
+ * TreeNode left;
+ * TreeNode right;
+ * TreeNode(int x) { val = x; }
+ * }
+ */
+class LeetCode_104_038 {
+ public int maxDepth(TreeNode root) {
+ if (root == null) {
+ return 0;
+ } else {
+ int left_height = maxDepth(root.left);
+ int right_height = maxDepth(root.right);
+ return java.lang.Math.max(left_height, right_height) + 1;
+ }
+ }
+
+ public static void main(String[] args) {
+ LeetCode_104_038 testCode_104_038 = new LeetCode_104_038();
+ System.out.println(testCode_104_038.maxDepth(nums));
+ }
+}
+
+public class TreeNode {
+ int val;
+ TreeNode left;
+ TreeNode right;
+
+ TreeNode(int x) {
+ val = x;
+ }
+ }
diff --git a/Week_01/id_38/README.md b/Week_01/id_38/README.md
index b11159e4..69b0ff78 100644
--- a/Week_01/id_38/README.md
+++ b/Week_01/id_38/README.md
@@ -3,63 +3,62 @@
## 第一周题目
---
### 数组、链表
-【简单】[26. 删除排序数组中的重复项 ](https://leetcode-cn.com/problems/remove-duplicates-from-sorted-array/)
+* [x] 【简单】[26. 删除排序数组中的重复项 ](https://leetcode-cn.com/problems/remove-duplicates-from-sorted-array/)
-【简单】[189. 旋转数组](https://leetcode-cn.com/problems/rotate-array/)
+* [ ] 【简单】[189. 旋转数组](https://leetcode-cn.com/problems/rotate-array/)
-【简单】[21. 合并两个有序链表](https://leetcode-cn.com/problems/merge-two-sorted-lists/)
+* [ ] 【简单】[21. 合并两个有序链表](https://leetcode-cn.com/problems/merge-two-sorted-lists/)
-【简单】[88. 合并两个有序数组](https://leetcode-cn.com/problems/merge-sorted-array/)
+* [ ] 【简单】[88. 合并两个有序数组](https://leetcode-cn.com/problems/merge-sorted-array/)
-【中等】[24. 两两交换链表中的节点](https://leetcode-cn.com/problems/swap-nodes-in-pairs/)
+* [ ] 【中等】[24. 两两交换链表中的节点](https://leetcode-cn.com/problems/swap-nodes-in-pairs/)
-【中等】[15. 三数之和](https://leetcode-cn.com/problems/3sum/)
+* [x] 【中等】[15. 三数之和](https://leetcode-cn.com/problems/3sum/)
---
### Map & Set
-[242. 有效的字母异位词【简单】](https://leetcode-cn.com/problems/valid-anagram/)
+* [x] [242. 有效的字母异位词【简单】](https://leetcode-cn.com/problems/valid-anagram/)
-[49. 字母异位词分组【中等】](https://leetcode-cn.com/problems/group-anagrams/)
+* [ ] [49. 字母异位词分组【中等】](https://leetcode-cn.com/problems/group-anagrams/)
---
### 堆栈、队列
-[1047. 删除字符串中的所有相邻重复项【简单】](https://leetcode-cn.com/problems/remove-all-adjacent-duplicates-in-string/)
+* [ ] [1047. 删除字符串中的所有相邻重复项【简单】](https://leetcode-cn.com/problems/remove-all-adjacent-duplicates-in-string/)
-[1021. 删除最外层的括号【简单】](https://leetcode-cn.com/problems/remove-outermost-parentheses/)
+* [ ] [1021. 删除最外层的括号【简单】](https://leetcode-cn.com/problems/remove-outermost-parentheses/)
-[84. 柱状图中最大的矩形【困难】](https://leetcode.com/problems/largest-rectangle-in-histogram/)
+* [ ] [84. 柱状图中最大的矩形【困难】](https://leetcode.com/problems/largest-rectangle-in-histogram/)
-[42. 接雨水【困难】](https://leetcode.com/problems/trapping-rain-water/)
+* [ ] [42. 接雨水【困难】](https://leetcode.com/problems/trapping-rain-water/)
---
### 二分查找
-[441. 排列硬币【简单】](https://leetcode-cn.com/problems/arranging-coins/)
+* [ ] [441. 排列硬币【简单】](https://leetcode-cn.com/problems/arranging-coins/)
-[50. Pow(x, n)【中等】](https://leetcode-cn.com/problems/powx-n/)
+* [x] [50. Pow(x, n)【中等】](https://leetcode-cn.com/problems/powx-n/)
-[174. 地下城游戏【困难】](https://leetcode-cn.com/problems/dungeon-game/)
+* [ ] [174. 地下城游戏【困难】](https://leetcode-cn.com/problems/dungeon-game/)
---
### 递归
-[104. 二叉树的最大深度【简单】](https://leetcode-cn.com/problems/maximum-depth-of-binary-tree/)
+* [ ] [104. 二叉树的最大深度【简单】](https://leetcode-cn.com/problems/maximum-depth-of-binary-tree/)
-[101. 对称二叉树【简单】](https://leetcode-cn.com/problems/symmetric-tree/)
+* [ ] [101. 对称二叉树【简单】](https://leetcode-cn.com/problems/symmetric-tree/)
-[111. 二叉树的最小深度【简单】](https://leetcode-cn.com/problems/minimum-depth-of-binary-tree/)
+* [ ] [111. 二叉树的最小深度【简单】](https://leetcode-cn.com/problems/minimum-depth-of-binary-tree/)
-[783. 二叉搜索树结点最小距离【简单】](https://leetcode-cn.com/problems/minimum-distance-between-bst-nodes/)
+* [ ] [783. 二叉搜索树结点最小距离【简单】](https://leetcode-cn.com/problems/minimum-distance-between-bst-nodes/)
-[257. 二叉树的所有路径【简单】](https://leetcode-cn.com/problems/binary-tree-paths/)
+* [ ] [257. 二叉树的所有路径【简单】](https://leetcode-cn.com/problems/binary-tree-paths/)
-[938. 二叉搜索树的范围和【简单】](https://leetcode-cn.com/problems/range-sum-of-bst/)
-
-[236. 二叉树的最近公共祖先【中等】](https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/)
+* [ ] [938. 二叉搜索树的范围和【简单】](https://leetcode-cn.com/problems/range-sum-of-bst/)
+* [ ] [236. 二叉树的最近公共祖先【中等】](https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/)
diff --git a/Week_02/id_38/LeetCode_01_038.java b/Week_02/id_38/LeetCode_01_038.java
new file mode 100644
index 00000000..dca4e70d
--- /dev/null
+++ b/Week_02/id_38/LeetCode_01_038.java
@@ -0,0 +1,66 @@
+import java.util.*;
+
+/*
+ * @lc app=leetcode.cn id=1 lang=java
+ *
+ * [1] 两数之和
+ */
+class LeetCode_01_038 {
+ public int[] twoSum(int[] nums, int target) {
+ // hashmap, 时间 O(n),空间 O(n)
+ Map numDic = new HashMap();
+ // push and process
+ for (int i = 0; i < nums.length; ++i) {
+ if (numDic.containsKey(target - nums[i])
+ && numDic.get(target - nums[i]) != i) {
+ return new int[]{numDic.get(target - nums[i]), i};
+ }
+ numDic.put(nums[i], i);
+ }
+
+ throw new IllegalArgumentException("No two sum solution");
+ }
+
+ public int[] twoSum1(int[] nums, int target) {
+ // hashmap, 时间 O(2n),空间 O(n)
+ Map numDic = new HashMap();
+ // push
+ for (int i = 0; i < nums.length; ++i) {
+ numDic.put(nums[i], i);
+ }
+
+ for (int i = 0; i < nums.length; ++i) {
+ if (numDic.containsKey(target - nums[i])
+ && numDic.get(target - nums[i]) != i) {
+ return new int[]{i, numDic.get(target - nums[i])};
+ }
+ }
+
+ throw new IllegalArgumentException("No two sum solution");
+ }
+
+ public int[] twoSum2(int[] nums, int target) {
+ // check valid
+
+ // 暴力，时间 O(n^2)，空间 O(1)
+ for (int i = 0; i < nums.length - 1; ++i) {
+ for (int j = i + 1; j < nums.length; ++j) {
+ if (nums[i] + nums[j] == target) {
+ return new int[]{i, j};
+ }
+ }
+ }
+
+ throw new IllegalArgumentException("No two sum solution");
+ }
+
+ public static void main(String[] args) {
+ LeetCode_01_038 testCode_01_038 = new LeetCode_01_038();
+ int[] nums = new int[]{-1};
+ int[] result = testCode_01_038.twoSum2(nums, 3);
+ for (int i = 0; i < result.length; ++i) {
+ System.out.print(result[i] + ",");
+ }
+ }
+}
+
diff --git a/Week_02/id_38/LeetCode_111_038.java b/Week_02/id_38/LeetCode_111_038.java
new file mode 100644
index 00000000..5871e376
--- /dev/null
+++ b/Week_02/id_38/LeetCode_111_038.java
@@ -0,0 +1,26 @@
+import java.util.*;
+
+/*
+ * @lc app=leetcode.cn id=111 lang=java
+ *
+ * [111] 二叉树的最小深度
+ */
+class LeetCode_111_038 {
+ public int minDepth(TreeNode root) {
+ if (root == null) return 0;
+ if ((root.l == null) && (root.r == null)) return 1;
+ if (root.l == null) return minDepth(root.r) + 1;
+ if (root.r == null) return minDepth(root.l) + 1;
+ return Math.min(minDepth(root.l), minDepth(root.r)) + 1;
+ }
+}
+
+class TreeNode {
+ int val;
+ TreeNode l;
+ TreeNode r;
+ TreeNode(int x) {
+ this.val = x;
+ }
+}
+
diff --git a/Week_02/id_38/LeetCode_242_038.java b/Week_02/id_38/LeetCode_242_038.java
new file mode 100644
index 00000000..fdec858b
--- /dev/null
+++ b/Week_02/id_38/LeetCode_242_038.java
@@ -0,0 +1,81 @@
+import java.util.Arrays;
+import java.util.List;
+
+/*
+ * @lc app=leetcode.cn id=242 lang=java
+ *
+ * [242] 有效的字母异位词
+ */
+class LeetCode_242_038 {
+
+ /**
+ * hash
+ * 执行用时：11ms，内存消耗：38.2mb
+ * 时间：O(n), 空间：O(1),n为字符串长度
+ * @param s
+ * @param t
+ * @return
+ */
+ public boolean isAnagram(String s, String t) {
+ // check valid
+ if (equals(s, t)) return true;
+ if (length(s) != length(t)) return false;
+
+ int[] charArr = new int[26];
+ for (int i = 0; i < s.length(); ++i) {
+ charArr[s.charAt(i) - 'a']++;
+ charArr[t.charAt(i) - 'a']--;
+ }
+
+ for (int i : charArr) {
+ if (i != 0) return false;
+ }
+ return true;
+ }
+
+ /**
+ * 将两string排序，然后判断是否相同
+ * 执行用时：317ms，内存消耗：58.2mb
+ * -。-
+ * 自行实现的算法效率正是低，代码也一大坨
+ * @param s
+ * @param t
+ * @return
+ */
+ public boolean isAnagram2(String s, String t) {
+ if (equals(s, t)) return true;
+ if (length(s) != length(t)) return false;
+
+ return equals(stringSort(s), stringSort(t));
+ }
+
+ public String stringSort(String s) {
+ if (isEmpty(s)) return s;
+ String[] sa = s.split("");
+ Arrays.sort(sa);
+ System.out.println(String.join("", sa));
+ return String.join("", sa);
+ }
+
+ public boolean isEmpty(String s) {
+ if (s == null || s.length() == 0) return true;
+ return false;
+ }
+
+ public boolean equals(String s, String t) {
+ if (isEmpty(s) && isEmpty(t)) return true;
+ if (!isEmpty(s) && s.equals(t)) return true;
+ return false;
+ }
+
+ public int length(String s) {
+ if (isEmpty(s)) return 0;
+ return s.length();
+ }
+
+ public static void main(String[] args) {
+ LeetCode_242_038 testCode_242_038 = new LeetCode_242_038();
+ System.out.print(testCode_242_038.isAnagram("ab", "ba"));
+ }
+}
+
diff --git a/Week_02/id_38/README.md b/Week_02/id_38/README.md
new file mode 100644
index 00000000..7f497f14
--- /dev/null
+++ b/Week_02/id_38/README.md
@@ -0,0 +1,48 @@
+# 学习笔记
+
+## 第二周题目
+---
+### 哈希表
+* [x] 【简单】[1. 两数之和 ](https://leetcode-cn.com/problems/two-sum/)
+
+* [ ] 【简单】[242. 有效的字母异位词](https://leetcode-cn.com/problems/valid-anagram/)
+
+* [ ] 【中等】[3. 无重复字符的最长子串](https://leetcode-cn.com/problems/longest-substring-without-repeating-characters)
+
+* [ ] 【中等】[692. 前K个高频单词](https://leetcode-cn.com/problems/top-k-frequent-words)
+
+* [ ] 【困难】[726. 原子的数量](https://leetcode-cn.com/problems/number-of-atoms/)
+
+---
+
+### 二叉树
+* [ ] [111. 二叉树的最小深度【简单】](https://leetcode-cn.com/problems/minimum-depth-of-binary-tree/)
+
+* [ ] [236. 二叉树的最近公共祖先【中等】](https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/)
+
+* [ ] [101. 对称二叉树【简单】](https://leetcode-cn.com/problems/symmetric-tree/)
+
+* [ ] [103. 二叉树的锯齿形层次遍历【中等】](https://leetcode-cn.com/problems/binary-tree-zigzag-level-order-traversal/)
+
+* [ ] [102. 二叉树的层次遍历【中等】](https://leetcode-cn.com/problems/binary-tree-level-order-traversal/)
+
+* [ ] [297. 二叉树的序列化与反序列化【困难】](https://leetcode-cn.com/problems/serialize-and-deserialize-binary-tree/)
+
+
+---
+
+### 二叉搜索树
+* [ ] [783. 二叉搜索树结点最小距离【简单】](https://leetcode-cn.com/problems/minimum-distance-between-bst-nodes/)
+
+* [ ] [235. 二叉搜索树的最近公共祖先【简单】](https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-search-tree/)
+
+* [ ] [98. 验证二叉搜索树【中等】](https://leetcode-cn.com/problems/validate-binary-search-tree/)
+
+* [ ] [938. 二叉搜索树的范围和【中等】](https://leetcode-cn.com/problems/range-sum-of-bst/)
+
+* [ ] [220. 存在重复元素 III【中等】](https://leetcode-cn.com/problems/contains-duplicate-iii/)
+
+* [ ] [315. 计算右侧小于当前元素的个数【困难】](https://leetcode-cn.com/problems/count-of-smaller-numbers-after-self/)
+
+
+---
\ No newline at end of file
diff --git a/Week_03/id_38/LeetCode_104_038.java b/Week_03/id_38/LeetCode_104_038.java
new file mode 100644
index 00000000..ed58b7a4
--- /dev/null
+++ b/Week_03/id_38/LeetCode_104_038.java
@@ -0,0 +1,29 @@
+/*
+ * @lc app=leetcode.cn id=104 lang=java
+ *
+ * [104] 二叉树的最大深度
+ */
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ * int val;
+ * TreeNode left;
+ * TreeNode right;
+ * TreeNode(int x) { val = x; }
+ * }
+ */
+class LeetCode_104_038 {
+ public int maxDepth(TreeNode root) {
+ return root == null ? 0 : Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
+ }
+}
+
+public class TreeNode {
+ int val;
+ TreeNode left;
+ TreeNode right;
+
+ TreeNode(int x) {
+ val = x;
+ }
+ }
diff --git a/Week_03/id_38/LeetCode_111_038.java b/Week_03/id_38/LeetCode_111_038.java
new file mode 100644
index 00000000..67556fd9
--- /dev/null
+++ b/Week_03/id_38/LeetCode_111_038.java
@@ -0,0 +1,25 @@
+import java.util.*;
+
+/*
+ * @lc app=leetcode.cn id=111 lang=java
+ *
+ * [111] 二叉树的最小深度
+ */
+class LeetCode_111_038 {
+ public int minDepth(TreeNode root) {
+ if (root == null) return 0;
+ if (root.l == null) return minDepth(root.r) + 1;
+ if (root.r == null) return minDepth(root.l) + 1;
+ return Math.min(minDepth(root.l), minDepth(root.r)) + 1;
+ }
+}
+
+class TreeNode {
+ int val;
+ TreeNode l;
+ TreeNode r;
+ TreeNode(int x) {
+ this.val = x;
+ }
+}
+
diff --git a/Week_03/id_38/LeetCode_200_038.java b/Week_03/id_38/LeetCode_200_038.java
new file mode 100644
index 00000000..56c75a9c
--- /dev/null
+++ b/Week_03/id_38/LeetCode_200_038.java
@@ -0,0 +1,51 @@
+/*
+ * @lc app=leetcode.cn id=200 lang=java
+ *
+ * [200] 岛屿数量
+ */
+class LeetCode_200_038 {
+ /**
+ * 染色
+ * @param grid
+ * @return
+ */
+ public int numIslands(char[][] grid) {
+ // check valid
+ if(grid == null || grid.length == 0) return 0;
+
+ int count = 0;
+ int col = grid[0].length;
+ int row = grid.length;
+ for(int i = 0; i < row; ++i) {
+ for(int j = 0; j < col; ++j) {
+ if(grid[i][j] == '1') {
+ count++;
+ bfs(i, j, grid);
+ }
+ }
+ }
+
+ return count;
+ }
+
+ public void bfs(int col, int row, char[][] grid) {
+ if(col < 0 || col >= grid.length) return;
+ if(row < 0 || row >= grid[0].length) return;
+ if(grid[col][row] == '1') {
+ grid[col][row] = '0';
+ bfs(col + 1, row, grid);
+ bfs(col, row + 1, grid);
+ bfs(col - 1, row, grid);
+ bfs(col, row - 1, grid);
+ }
+ }
+
+ public static void main(String[] args) {
+ LeetCode_200_038 testCode_200_038 = new LeetCode_200_038();
+ char[][] grid = new char[][]{{'1', '1', '1', '1', '0'},
+ {'1', '1', '0', '1', '0'},
+ {'1', '1', '0', '0', '0'},
+ {'0', '0', '0', '0', '0'}};
+ System.out.println(testCode_200_038.numIslands(grid));
+ }
+}
\ No newline at end of file
diff --git a/Week_03/id_38/LeetCode_703_038.java b/Week_03/id_38/LeetCode_703_038.java
new file mode 100644
index 00000000..64ae1677
--- /dev/null
+++ b/Week_03/id_38/LeetCode_703_038.java
@@ -0,0 +1,40 @@
+/*
+ * @lc app=leetcode.cn id=703 lang=java
+ *
+ * [703] 数据流中的第K大元素
+ */
+class LeetCode_703_038 {
+
+ public static void main(String[] args) {
+ KthLargest kthLargest = new KthLargest(3, new int[]{1, 2, 4, 9});
+ System.out.println(kthLargest.add(3));
+ System.out.println(kthLargest.add(0));
+ System.out.println(kthLargest.add(8));
+ }
+}
+
+/**
+ * 优先队列
+ */
+class KthLargest {
+
+ final PriorityQueue pq;
+ final int k;
+ public KthLargest(int k, int[] nums) {
+ this.k = k;
+ pq = new PriorityQueue<>(k);
+ for(int i : nums) {
+ add(i);
+ }
+ }
+
+ public int add(int val) {
+ if(pq.size() < k) {
+ pq.offer(val);
+ }else if(pq.peek() < val) {
+ pq.poll();
+ pq.offer(val);
+ }
+ return pq.peek();
+ }
+}
\ No newline at end of file
diff --git a/Week_03/id_38/README.md b/Week_03/id_38/README.md
new file mode 100644
index 00000000..34d9e3de
--- /dev/null
+++ b/Week_03/id_38/README.md
@@ -0,0 +1,29 @@
+# 学习笔记
+
+## 第三周题目
+---
+
+### 图
+* [x] 【中等】[200. 岛屿数量](https://leetcode-cn.com/problems/number-of-islands/)
+* [ ] 【中等】[210. 课程表 II](https://leetcode-cn.com/problems/course-schedule-ii)
+---
+### 堆和排序
+* [x] 【简单】[703. 数据流中的第K大元素](https://leetcode-cn.com/problems/kth-largest-element-in-a-stream/)
+* [ ] 【困难】[295. 数据流的中位数](https://leetcode-cn.com/problems/find-median-from-data-stream/)
+---
+### DFS
+* [x] 【简单】[104. 二叉树的最大深度](https://leetcode-cn.com/problems/maximum-depth-of-binary-tree/)
+* [x] 【简单】[111. 二叉树的最小深度](https://leetcode-cn.com/problems/minimum-depth-of-binary-tree/)
+* [ ] 【中等】[547. 朋友圈](https://leetcode-cn.com/problems/friend-circles/)
+* [ ] 【中等】[802. 找到最终的安全状态](https://leetcode-cn.com/problems/find-eventual-safe-states/)
+* [ ] 【困难】[329. 矩阵中的最长递增路径](https://leetcode-cn.com/problems/longest-increasing-path-in-a-matrix/)
+* [ ] 【中等】[529. 扫雷游戏](https://leetcode-cn.com/problems/minesweeper/)
+* [ ] 【困难】[127. 单词接龙](https://leetcode-cn.com/problems/word-ladder/)
+---
+### BFS
+* [ ] 【简单】[429. N叉树的层序遍历](https://leetcode-cn.com/problems/n-ary-tree-level-order-traversal/)
+* [ ] 【中等】[102. 二叉树的层次遍历](https://leetcode-cn.com/problems/binary-tree-level-order-traversal/)
+* [ ] 【简单】[107. 二叉树的层次遍历 II](https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii/)
+* [ ] 【中等】[103. 二叉树的锯齿形层次遍历](https://leetcode-cn.com/problems/binary-tree-zigzag-level-order-traversal/)
+* [ ] 【中等】[529. 扫雷游戏](https://leetcode-cn.com/problems/minesweeper/)
+* [ ] 【中等】[310. 最小高度树](https://leetcode-cn.com/problems/minimum-height-trees/)