16. Check if it is BST

Title Description

Implement a function to check whether a binary tree is a two-fork lookup tree.

The root node pointer of the given tree treenode* root, returns a bool that represents whether the tree is a two-fork lookup tree

Import Java.util.*;/*public class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    Public TreeNode (int val) {        this.val = val;    }} */public class Checker {public    Boolean checkbst (TreeNode root) {        if (root==null) return true;        Boolean b1=checkbst (root.left);        Boolean b2= Checkbst (root.right);        if (B1 && b2) {            if (root.left!=null && root.left.val>root.val)                return false;            if (root.right!=null && root.right.val<root.val)                return false;            return true;        } else            return false;}    }

　　

16. Check if it is BST