[leetcode] Validate Binary Search Tree

Given a binary tree, determine if it is a valid binary search tree (BST).

Assume a BST is defined as follows:

  • The left subtree of a node contains only nodes with keys less than the node’s key.
  • The right subtree of a node contains only nodes with keys greater than the node’s key.
  • Both the left and right subtrees must also be binary search trees.

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

 * 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 {
    bool isValidBST(TreeNode* root) {
        if(root == NULL){
            return true;
            return _isValidBST(root->left, LONG_MIN, root->val) && _isValidBST(root->right, (long)root->val + 1, LONG_MAX);
    bool _isValidBST(TreeNode * root, long min, long max){
        if(root == NULL){
            return true;
        if(root->val < min || root->val >= max){
            return false;
            return _isValidBST(root->left, min, root->val) && _isValidBST(root->right, (long)root->val + 1, max);



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