Given a binary tree, return true if it is BST, else false. For example, the following tree is not BST, because 11 is in the left subtree of 10. The task is to complete the function isBST() which takes one argument, root of Binary Tree.

     /     \
   7       39

The first line of input contains the number of test cases T. Each test case contains a string representing the tree as described below: 

  1. The values in the string are in the order of level order traversal of the tree where, numbers denote node values, and a character “N” denotes NULL child.

  2. For example:
    For the above tree, the string will be: 1 2 3 N N 4 6 N 5 N N 7 N

The function should return 1 if BST else returns 0.

Your Task:
Since this is a functional problem you don't have to worry about input, you just have to complete the function isBST() which takes the root of the tree as a parameter.

1 <= T <= 10
0 <= Number of edges <= 100000


2 1 3
2 N 7 N 6 N 5 N 9 N 2 N 6

Testcase 1:
The given binary tree is a BST, hence the answer is 1.

Note: The Input/Output format and Example are given are used for the system's internal purpose, and should be used by a user for Expected Output only. As it is a function problem, hence a user should not read any input from the stdin/console. The task is to complete the function specified, and not to write the full code.

** For More Input/Output Examples Use 'Expected Output' option **

Contributor: Amit Khandelwal, Harshit Sidhwa
Author: kartik

If you have purchased any course from GeeksforGeeks then please ask your doubt on course discussion forum. You will get quick replies from GFG Moderators there.

Need help with your code? Please use, generate link and share the link here.

to report an issue on this page.