✨feat: Add 652

Index/DFS.md

@@ -31,6 +31,7 @@
 | [606. 根据二叉树创建字符串](https://leetcode-cn.com/problems/construct-string-from-binary-tree/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/construct-string-from-binary-tree/solution/by-ac_oier-i2sk/) | 简单 | 🤩🤩🤩🤩     |
 | [623. 在二叉树中增加一行](https://leetcode.cn/problems/add-one-row-to-tree/) | [LeetCode 题解链接](https://leetcode.cn/problems/add-one-row-to-tree/solution/by-ac_oier-sc34/) | 中等 | 🤩🤩🤩🤩     |
 | [638. 大礼包](https://leetcode-cn.com/problems/shopping-offers/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/shopping-offers/solution/gong-shui-san-xie-yi-ti-shuang-jie-zhuan-qgk1/) | 中等 | 🤩🤩🤩🤩     |
+| [652. 寻找重复的子树](https://leetcode.cn/problems/find-duplicate-subtrees/) | [LeetCode 题解链接](https://leetcode.cn/problems/find-duplicate-subtrees/solution/by-ac_oier-ly58/) | 中等 | 🤩🤩🤩🤩     |
 | [653. 两数之和 IV - 输入 BST](https://leetcode-cn.com/problems/two-sum-iv-input-is-a-bst/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/two-sum-iv-input-is-a-bst/solution/by-ac_oier-zr4o/) | 简单 | 🤩🤩🤩🤩     |
 | [654. 最大二叉树](https://leetcode.cn/problems/maximum-binary-tree/) | [LeetCode 题解链接](https://leetcode.cn/problems/maximum-binary-tree/solution/by-ac_oier-s0wc/) | 中等 | 🤩🤩🤩🤩🤩    |
 | [655. 输出二叉树](https://leetcode.cn/problems/print-binary-tree/) | [LeetCode 题解链接](https://leetcode.cn/problems/print-binary-tree/solution/by-ac_oier-mays/) | 中等 | 🤩🤩🤩🤩     |

Index/二叉树.md

@@ -9,6 +9,7 @@
 | [563. 二叉树的坡度](https://leetcode-cn.com/problems/binary-tree-tilt/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/binary-tree-tilt/solution/gong-shui-san-xie-jian-dan-er-cha-shu-di-ekz4/) | 简单 | 🤩🤩🤩🤩     |
 | [606. 根据二叉树创建字符串](https://leetcode-cn.com/problems/construct-string-from-binary-tree/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/construct-string-from-binary-tree/solution/by-ac_oier-i2sk/) | 简单 | 🤩🤩🤩🤩     |
 | [623. 在二叉树中增加一行](https://leetcode.cn/problems/add-one-row-to-tree/) | [LeetCode 题解链接](https://leetcode.cn/problems/add-one-row-to-tree/solution/by-ac_oier-sc34/) | 中等 | 🤩🤩🤩🤩     |
+| [652. 寻找重复的子树](https://leetcode.cn/problems/find-duplicate-subtrees/) | [LeetCode 题解链接](https://leetcode.cn/problems/find-duplicate-subtrees/solution/by-ac_oier-ly58/) | 中等 | 🤩🤩🤩🤩     |
 | [653. 两数之和 IV - 输入 BST](https://leetcode-cn.com/problems/two-sum-iv-input-is-a-bst/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/two-sum-iv-input-is-a-bst/solution/by-ac_oier-zr4o/) | 简单 | 🤩🤩🤩🤩     |
 | [654. 最大二叉树](https://leetcode.cn/problems/maximum-binary-tree/) | [LeetCode 题解链接](https://leetcode.cn/problems/maximum-binary-tree/solution/by-ac_oier-s0wc/) | 中等 | 🤩🤩🤩🤩🤩    |
 | [655. 输出二叉树](https://leetcode.cn/problems/print-binary-tree/) | [LeetCode 题解链接](https://leetcode.cn/problems/print-binary-tree/solution/by-ac_oier-mays/) | 中等 | 🤩🤩🤩🤩     |

Index/哈希表.md

@@ -34,6 +34,7 @@
 | [594. 最长和谐子序列](https://leetcode-cn.com/problems/longest-harmonious-subsequence/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/longest-harmonious-subsequence/solution/gong-shui-san-xie-yi-ti-shuang-jie-hua-d-quuh/) | 简单 | 🤩🤩🤩🤩 |
 | [599. 两个列表的最小索引总和](https://leetcode-cn.com/problems/minimum-index-sum-of-two-lists/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/minimum-index-sum-of-two-lists/solution/by-ac_oier-oh5b/) | 简单 | 🤩🤩🤩🤩 |
 | [645. 错误的集合](https://leetcode-cn.com/problems/set-mismatch/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/set-mismatch/solution/gong-shui-san-xie-yi-ti-san-jie-ji-shu-s-vnr9/) | 简单 | 🤩🤩🤩 |
+| [652. 寻找重复的子树](https://leetcode.cn/problems/find-duplicate-subtrees/) | [LeetCode 题解链接](https://leetcode.cn/problems/find-duplicate-subtrees/solution/by-ac_oier-ly58/) | 中等 | 🤩🤩🤩🤩 |
 | [653. 两数之和 IV - 输入 BST](https://leetcode-cn.com/problems/two-sum-iv-input-is-a-bst/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/two-sum-iv-input-is-a-bst/solution/by-ac_oier-zr4o/) | 简单 | 🤩🤩🤩🤩 |
 | [662. 二叉树最大宽度](https://leetcode.cn/problems/maximum-width-of-binary-tree/) | [LeetCode 题解链接](https://leetcode.cn/problems/maximum-width-of-binary-tree/solution/by-ac_oier-33er/) | 中等 | 🤩🤩🤩🤩 |
 | [677. 键值映射](https://leetcode-cn.com/problems/map-sum-pairs/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/map-sum-pairs/solution/gong-shui-san-xie-jie-he-dfs-de-trie-yun-i4xa/) | 中等 | 🤩🤩🤩🤩 |

LeetCode/651-660/652. 寻找重复的子树（中等）.md

@@ -0,0 +1,107 @@
+### 题目描述
+
+这是 LeetCode 上的 **[652. 寻找重复的子树](https://leetcode.cn/problems/find-duplicate-subtrees/solution/by-ac_oier-ly58/)** ，难度为 **中等**。
+
+Tag : 「二叉树」、「哈希表」、「DFS」
+
+
+
+给定一棵二叉树 `root`，返回所有重复的子树。
+
+对于同一类的重复子树，你只需要返回其中任意一棵的根结点即可。
+
+如果两棵树具有相同的结构和相同的结点值，则它们是重复的。
+
+示例 1：
+![](https://assets.leetcode.com/uploads/2020/08/16/e1.jpg)
+```
+输入：root = [1,2,3,4,null,2,4,null,null,4]
+
+输出：[[2,4],[4]]
+```
+示例 2：
+![](https://assets.leetcode.com/uploads/2020/08/16/e2.jpg)
+```
+输入：root = [2,1,1]
+
+输出：[[1]]
+```
+示例 3：
+![](https://assets.leetcode.com/uploads/2020/08/16/e33.jpg)
+```
+输入：root = [2,2,2,3,null,3,null]
+
+输出：[[2,3],[3]]
+```
+
+提示：
+* 树中的结点数在 $[1,10^4]$ 范围内。
+* $-200 <= Node.val <= 200$
+
+---
+
+### DFS + 哈希表
+
+设计递归函数 `String dfs(TreeNode root)`，含义为返回以传入参数 `root` 为根节点的子树所对应的指纹标识。
+
+对于标识的设计只需使用 `"_"` 分割不同的节点值，同时对空节点进行保留（定义为空串 `" "`）即可。
+
+使用哈希表记录每个标识（子树）出现次数，当出现次数为 $2$（首次判定为重复出现）时，将该节点加入答案。
+
+Java 代码：
+```Java
+class Solution {
+    Map<String, Integer> map = new HashMap<>();
+    List<TreeNode> ans = new ArrayList<>();
+    public List<TreeNode> findDuplicateSubtrees(TreeNode root) {
+        dfs(root);
+        return ans;
+    }
+    String dfs(TreeNode root) {
+        if (root == null) return " ";
+        StringBuilder sb = new StringBuilder();
+        sb.append(root.val).append("_");
+        sb.append(dfs(root.left)).append(dfs(root.right));
+        String key = sb.toString();
+        map.put(key, map.getOrDefault(key, 0) + 1);
+        if (map.get(key) == 2) ans.add(root);
+        return key;
+    }
+}
+```
+Typescript 代码：
+```Typescript
+let ans: Array<TreeNode>
+let map: Map<string, number>
+function findDuplicateSubtrees(root: TreeNode | null): Array<TreeNode | null> {
+    ans = new Array<TreeNode>()
+    map = new Map<string, number>()
+    dfs(root)
+    return ans
+};
+function dfs(root: TreeNode | null): string {
+    if (root == null) return " "
+    let key = root.val + "_"
+    key += dfs(root.left)
+    key += dfs(root.right)
+    if (!map.has(key)) map.set(key, 1)
+    else map.set(key, map.get(key) + 1)
+    if (map.get(key) == 2) ans.push(root)
+    return key
+}
+```
+* 时间复杂度：`DFS` 过程复杂度为 $O(n)$，对于每个子树需要构造出与子树同等规模的字符串，复杂度为 $O(n)$。整体复杂度为 $O(n^2)$
+* 空间复杂度：$O(n)$
+
+---
+
+### 最后
+
+这是我们「刷穿 LeetCode」系列文章的第 `No.652` 篇，系列开始于 2021/01/01，截止于起始日 LeetCode 上共有 1916 道题目，部分是有锁题，我们将先把所有不带锁的题目刷完。
+
+在这个系列文章里面，除了讲解解题思路以外，还会尽可能给出最为简洁的代码。如果涉及通解还会相应的代码模板。
+
+为了方便各位同学能够电脑上进行调试和提交代码，我建立了相关的仓库：https://github.com/SharingSource/LogicStack-LeetCode 。
+
+在仓库地址里，你可以看到系列文章的题解链接、系列文章的相应代码、LeetCode 原题链接和其他优选题解。
+