9.md

Validate BST

bool find(TreeNode* root, long long min,long long max)
    {
          if (root == NULL)
        return true;

    if (root->val <= min || root->val >= max)
        return false;

    // Check left subtree with updated max_val
    bool left_valid = find(root->left, min, root->val);
    
    // Check right subtree with updated min_val
    bool right_valid = find(root->right, root->val, max);

    return left_valid && right_valid;
    }

    bool isValidBST(TreeNode* root) {
        
      return find(root,LONG_MIN,LONG_MAX);
}