LeetCode Problem : Validate Binary Search Tree

Problem 

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.


OJ's Binary Tree Serialization:
The serialization of a binary tree follows a level order traversal, where '#' signifies a path terminator where no node exists below.

Here's an example:
   1
  / \
 2   3
    /
   4
    \
     5
The above binary tree is serialized as "{1,2,3,#,#,4,#,#,5}".

Code

bool isvbst_r(TreeNode *root,int min,int max)
{
    if(!root)
        return true;
    if(root->val <= min || root->val >= max)
        return false;
    return (isvbst_r(root->right,root->val,max) && 
    isvbst_r(root->left,min,root->val));
}
bool isValidBST(TreeNode *root) {
// IMPORTANT: Please reset any member data you declared, as
// the same Solution instance will be reused for each test case.
    return isvbst_r(root,INT_MIN,INT_MAX);
}