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.

Just the property of bst, trick with long_min and max

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    bool isValidBST(TreeNode *root) {        return helper(root, LONG_MIN,LONG_MAX);    }        bool helper(TreeNode* root, long min, long max){        if (root==0)            return true;        if (root->val<=min || root->val>=max)            return false;        return helper(root->left, min,root->val ) && helper(root->right, root->val, max);    }};