[leetcode] Validate Binary Search Tree

public class Solution {

    public boolean isValidBST(TreeNode root) {
        return check(root, Integer.MIN_VALUE, Integer.MAX_VALUE);
    }

    private boolean check(TreeNode root, int min, int max) {
        if (root == null)
            return true;
        if (root.val >= max || root.val <= min)
            return false;
        return check(root.left, min, root.val) && check(root.right, root.val, max);

    }

    public static void main(String[] args) {
        TreeNode root = new TreeNode(10);
        root.left = new TreeNode(5);
        root.left.right = new TreeNode(9);
        root.right = new TreeNode(20);
        root.right.left = new TreeNode(11);

        System.out.println(new Solution().isValidBST(root));

    }

}