剑指 Offer 54. 二叉搜索树的第k大节点

思路

 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 private:
12     int cnt = 0;
13 public:
14     int kthLargest(TreeNode* root, int k) {
15         int res;
16         inOrderTraverse(root, k, res);
17 
18         return res;
19     }
20 
21     void inOrderTraverse(TreeNode *root, int k, int& res) {
22         if(cnt == k || root == NULL)
23             return;
24         inOrderTraverse(root->right, k, res);
25         cnt++;
26         if(cnt == k) {
27             res = root->val;
28             return;
29         }
30         inOrderTraverse(root->left, k, res);
31         
32     }
33 };