501. Find Mode in Binary Search Tree

Posted 2020-11-10 高数考了59

 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 static int wing=[]()
11 {
12     std::ios::sync_with_stdio(false);
13     cin.tie(NULL);
14     return 0;
15 }();
16 
17 class Solution 
18 {
19 public:
20     vector<int> findMode(TreeNode* root) 
21     {
22         vector<int> res;
23         if(root==NULL)
24             return res;
25         queue<TreeNode*> q;
26         int maxcount=0;
27         TreeNode *p=root;
28         q.push(p);
29         unordered_map<int,int> itoi;
30         while(!q.empty())
31         {
32             p=q.front();
33             itoi[p->val]++;
34             maxcount=max(maxcount,itoi[p->val]);
35             q.pop();
36             if(p->left)
37                 q.push(p->left);
38             if(p->right)
39                 q.push(p->right);
40         }       
41         for(auto k:itoi)
42             if(k.second==maxcount)
43                 res.push_back(k.first);
44         return res;
45     }
46 };

层次遍历，问题不大。可惜要用个辅助map，空间复杂度为O(n)