https://leetcode.com/problems/find-mode-in-binary-search-tree/

1. Use BST:

  1. //24 ms    20.8 MB
  3. /**
  4.  * Definition for a binary tree node.
  5.  * struct TreeNode {
  6.  *     int val;
  7.  *     TreeNode *left;
  8.  *     TreeNode *right;
  9.  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
  10.  * };
  11.  */
  12. class Solution {
  13. public:
  14.     vector<int> findMode(TreeNode* root) {
  15.         vector<int> result;
  17.         int val_ = 0;
  18.         int count_ = 0;  
  19.         int max_count_ = 0;
  21.         inorder(root, result, val_, count_, max_count_);
  23.         return result;
  24.     }
  26.     //the mode numbers in the binary tree are all connected 
  27.     void inorder(TreeNode* root, vector<int>& result, int& val_, int& count_, int& max_count_){
  28.         if(!root) return;
  30.         inorder(root->left, result, val_, count_, max_count_);
  32.         if (count_ > 0 && root->val == val_) {
  33.             count_++;   
  34.         } else {
  35.             val_ = root->val;
  36.             count_ = 1;
  37.         }
  39.         if (count_ > max_count_) {
  40.             max_count_ = count_;
  41.             result.clear();
  42.         }
  44.         if (count_ == max_count_)
  45.             result.push_back(root->val);
  47.         inorder(root->right, result, val_, count_, max_count_);
  48.     }
  51. };