剑指 Offer II 053. 二叉搜索树中的中序后继

https://leetcode.cn/problems/P5rCT8/

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* inorderSuccessor(TreeNode* root, TreeNode* p) {
        if(!root || !p) return NULL; 
        TreeNode  *next = NULL;
        if(p->right) {
            next = p->right;
            while(next->left) next = next->left;
            return next;
        }
        TreeNode *cur = root;
        while(cur->val != p->val) {
            if(p->val < cur->val) {
                next = cur;
                cur = cur ->left;
            } else {
                cur = cur->right;
            }
        }
        return next;
    }
};