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class Node

{

int data;

Node left, right;

public Node(int item)

{

data = item;

left = right = null;

}

}

public class ValidBSTOrNot

{

//Root of the Binary Tree

Node root;

/* can give min and max value according to your code or

can write a function to find min and max value of tree. */

/* returns true if given search tree is binary

search tree (efficient version) */

boolean isBST() {

return isBSTUtil(root, Integer.MIN_VALUE,

Integer.MAX_VALUE);

}

/* Returns true if the given tree is a BST and its

values are >= min and <= max. */

boolean isBSTUtil(Node node, int min, int max)

{

/* an empty tree is BST */

if (node == null)

return true;

/* false if this node violates the min/max constraints */

if (node.data < min || node.data > max)

return false;

/* otherwise check the subtrees recursively

tightening the min/max constraints */

// Allow only distinct values

return (isBSTUtil(node.left, min, node.data-1) &&

isBSTUtil(node.right, node.data+1, max));

}

/* Driver program to test above functions */

public static void main(String args[])

{

ValidBSTOrNot tree = new ValidBSTOrNot();

tree.root = new Node(4);

tree.root.left = new Node(2);

tree.root.right = new Node(5);

tree.root.left.left = new Node(1);

tree.root.left.right = new Node(3);

if (tree.isBST())

System.out.println("IS BST");

else

System.out.println("Not a BST");

}

}