[LeetCode] 230. Kth Smallest Element in a BST 解题思路

 1     void visit(TreeNode* node){
 2         
 3         if (node->left != NULL){
 4             visit(node->left);
 5         }
 6         
 7         if (cnt == 0) {
 8             return;
 9         }
10         
11         cnt--;
12         if(cnt == 0){
13             res = node->val;
14             return ;
15         }
16         
17         if(node->right != NULL){
18             visit(node->right);
19         }
20     }
21 
22     int cnt;
23     int res;
24 
25     int kthSmallest(TreeNode* root, int k) {
26         cnt = k;
27         if(root == NULL){
28             return 0;
29         }
30         visit(root);
31         
32         return (cnt == 0) ? res : 0;
33     }