LeetCode 98. 验证二叉搜索树

 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     long minnum=LONG_MIN; 
13     bool flag=true;
14     bool isValidBST(TreeNode* root) {
15         if(root==NULL) return true;
16         if(flag&&root->left) isValidBST(root->left);
17         if(root->val<=minnum) flag=false;
18         minnum=root->val; 
19         if(flag&&root->right) isValidBST(root->right);
20         return flag;
21     }
22 };