Valid Binary Search Tree

Given a BST, give an approach to verify if it is a 'valid' BST. Code it.


Answer:

Solution I:

bool IsValidBST(TreeNode* n)
{
    if(n)
    {
        bool isLeftValid = true;
        bool isRightValid = true;
        if( n->left )
        {
            if (n->left->val > n->val)
                return false;
            isLeftValid = isValidBST(n->left);

        }
        if( n->right)
        {
            if (n->right->val <= n->val)
                return false;
            isRightValid = isValidBST(n->right);
        }
        return isLeftValid && isRightValid;
    }
    return true;
}