import java.lang.*;
import java.util.*;
import node.*;

class ValidateTree {
	public static boolean isValidBST(TreeNode root) {
		if (root.left == null || root.right == null)
			return true;
		else if (root.left.val > root.val || root.right.val < root.val)
			return false;
		boolean l = isValidBST(root.left);
		boolean r = isValidBST(root.right);
		return l && r ? true : false;
	}

	public static void main(String[] args) {
		TreeNode leftLeaf = new TreeNode(1);
		TreeNode middleLeaf = new TreeNode(3);
		TreeNode rightLeaf = new TreeNode(6);
		TreeNode rightParent = new TreeNode(4);
		TreeNode root = new TreeNode(5, leftLeaf, rightParent);
		System.out.println(isValidBST(root));
	}
}