【树】652. 寻找重复的子树

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     vector<TreeNode*> findDuplicateSubtrees(TreeNode* root) 
13     {
14         vector<TreeNode*> res;
15         unordered_map<string, int> mp;
16 
17         dfs(root, res, mp);
18         
19         return res;
20     }
21     
22     string dfs(TreeNode* root, vector<TreeNode*>& res, unordered_map<string, int>& mp)
23     {
24         if(root==0) 
25         {
26             return "";
27         }
28         //二叉树先序序列化
29         string str = to_string(root->val) + "," + dfs(root->left, res, mp) + "," + dfs(root->right, res, mp);
30         
31         if(mp[str] == 1)
32         {
33             res.push_back(root);
34         } 
35 
36         mp[str]++;
37         return str;
38     }
39 };