[LeetCode] Inorder Successor in BST

 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     TreeNode* inorderSuccessor(TreeNode* root, TreeNode* p) {
13         if (p == NULL) return NULL;
14         TreeNode *res = NULL;
15         if (p->right != NULL) {
16             res = p->right;
17             while (res->left) res = res->left;
18             return res;
19         }
20         TreeNode *q = root;
21         while (q != NULL && q->val != p->val) {
22             if (q->val > p->val) {
23                 res = q;
24                 q = q->left;
25             } else {
26                 q = q->right;
27             }
28         }
29         return res;
30     }
31 };