/* All Contributors (C) 2021 */
package io.github.poorguy.explore.learn.recursion2;

/**
 * Definition for a binary tree node. public class TreeNode { int val; TreeNode left; TreeNode
 * right; TreeNode() {} TreeNode(int val) { this.val = val; } TreeNode(int val, TreeNode left,
 * TreeNode right) { this.val = val; this.left = left; this.right = right; } }
 */
public class ValidateBinarySearchTree {
    public boolean isValidBST(TreeNode root) {
        return helper(root, Long.MIN_VALUE, Long.MAX_VALUE);
    }

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