.cc

/**
 * 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* target_successor;
    TreeNode* target;
    bool findTargetFlag;
    TreeNode* inorderSuccessor(TreeNode* root, TreeNode* p) {
        findTargetFlag = false;
        target = p;
        recursive(root);
        return target_successor;
    }
    void recursive(TreeNode* cur) {
        if(cur == NULL) return;
        recursive(cur->left);
        if(findTargetFlag && target_successor == NULL) {
            target_successor = cur;
        }
        if(cur->val == target->val) findTargetFlag = true;
        recursive(cur->right);
    }
};