Validate Binary Search Tree @LeetCode

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.

Example 1:
    2
   / \
  1   3
Binary tree [2,1,3], return true.

Example 2:
    1
   / \
  2   3
Binary tree [1,2,3], return false.

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SIMPLE c++ IMPLEMENTATION :( Recursive Solution )
--------------------------------------------------------------------------------

/**
 * 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 {
public:
    bool isValidBST(TreeNode* root) {
        return IsValidBSTree(root,NULL,NULL) ;
    }
   
    bool IsValidBSTree(TreeNode* root,TreeNode* min,TreeNode* max){
        if(root==NULL)
            return true ;
           
        if(min&&root->val<=min->val)
            return false ;
        if(max&&root->val>=max->val)
            return false ;
           
        return (IsValidBSTree(root->left,min,root)&&IsValidBSTree(root->right,root,max)) ;
    }
};

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