Is the binary tree BST

Problem

Find whether a given binary tree is a binary search tree or not.

Solution

We create a recursive function which takes max and min limit for its value. First the given root is tried within the range Integer.MAX and Integer.MIN. If they are fine for a BST, then this recursive function is tried for left and right subtree. When we try for left child the upper limit is the value of current node and whatever min is passed from parent. For right side min is the node's value and max is the given max passed by its parent.

Code

public class CheckForBST
{

 /**
  * @param args
  */
 public static void main(String[] args)
 {
  Node a=new Node(12);
  Node b=new Node(3);
  Node c=new Node(15);
  Node d=new Node(10);
  Node e=new Node(14);
  Node f=new Node(17);
  Node g=new Node(4);
  Node h=new Node(11);
  Node i=new Node(5);
  a.left=b;
  a.right=c;
  b.right=d;
  c.left=e;
  c.right=f;
  d.left=g;
  d.right=h;
  g.right=i;
  System.out.println(isBST(a));

 }

 public static boolean isBST(Node root)
 {
  return checkBooleanAndReturn(root, Integer.MAX_VALUE, 
    Integer.MIN_VALUE);
 }
 
 private static boolean checkBooleanAndReturn(Node root, 
  int max,int min)
 {
  if(root==null)return true;
  boolean leftOk=true;
  boolean rightOk=true;
  boolean centerOk=true;
  if(root.left!=null)
   leftOk=checkBooleanAndReturn(root.left,
    root.value,min);
  if(root.value>=min &&root.value<=max)
   centerOk=true;
  else
   centerOk=false;
  if(root.right!=null)
   rightOk=checkBooleanAndReturn(root.right,
    max,root.value);
  return leftOk&&centerOk&&rightOk;
 }
 

 static class Node
 {
  public Node left;
  public Node right;
  public int value;
  public Node(int value)
  {
   this.value=value;
  }
 }
}