LeetCode OJ:Validate Binary Search Tree

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 binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    bool dfs(TreeNode *root,int left,int right){        if(!root)return true;        return left<root->val&&right>root->val&&dfs(root->left,left,root->val)&&dfs(root->right,root->val,right);    }    bool isValidBST(TreeNode *root) {        if(root==NULL)return true;        return dfs(root,INT_MIN,INT_MAX);    }};