package code;
/*
 * 98. Validate Binary Search Tree
 * 
 * Medium
 * Tree, Depth-first Search
 * 
 * Tipsval
 */
import java.util.Stack;

public class lc98 {
    public static void main(String[] args) {
        TreeNode tn1 = new TreeNode(0);
        tn1.left = new TreeNode(-1);
        //System.out.println(isValidBST(tn1));
        System.out.println(isValidBST2(tn1));
    }
    public static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int x) { val = x; }
    }
    public static boolean isValidBST(TreeNode root) {
        if(root==null)
            return true;
        return dfs(root, -Double.MAX_VALUE, Double.MAX_VALUE);  // Double.MIN_VALUE0
    }
    public static boolean dfs(TreeNode root, double min_bound, double max_bound){   //
        if (root == null) return true;
        if (root.val >= max_bound || root.val