cousin java

// http://code2begin.blogspot.com
// program to print if 2 nodes of a binary tree are cousins or not

/**
 * Created by MOHIT on 25-05-2018.
 */

import java.io.*;
import java.util.*;

import static java.lang.Integer.max;


// node class
class node{
    int data;
    node left;
    node right;

    // function that returns a pointer to new node
    public node(int element){
        this.data = element;
        this.left = null;
        this.right = null;

    }
};


public class BinaryTree {


    static int level_of_node(node root, int data){
        return level_of_node_helper(root, data, -1);
    }


    // function to find and return the level of a node in binary tree
    static int level_of_node_helper(node root, int data, int level){
        // if the tree is isEmpty or if we reach a leaf node then return 0
        if (root == null){
            return -1;
        }
        if(root.data == data){
            return level+1;
        }

        // check in the left subtree for the element
        // if found then return the level
        int level_node = level_of_node_helper(root.left, data, level + 1);
        if (level_node != -1){
            return level_node;
        }

        // searching for the node in right subtree
        level_node = level_of_node_helper(root.right, data, level + 1);
        return level_node;

    }


    // function to check if 2 nodes are siblings or not
    static boolean isSibling(node parent, int n1, int n2){
        if(parent == null){
            return false;
        }
        if(parent.left != null && parent.right != null) {
            return  (parent.left.data == n1 && parent.right.data == n2) ||
                    (parent.left.data == n2 && parent.right.data == n1);
        }
        return (isSibling(parent.left, n1, n2) || isSibling(parent.right, n1, n2));
    }

    static boolean isCousin(node root, int a, int b){
        if( (level_of_node(root, a) == level_of_node(root, b) && isSibling(root, a, b))){
            return true;
        }
        return false;
    }


    public static void main(String arg[]) {
        node head = new node(1);
        head.left = new node(2);
        head.right = new node(3);
        head.left.left = new node(4);
        head.left.right = new node(5);
        head.right.right = new node(6);
        head.left.left.right = new node(7);
        head.right.right.left = new node(8);
        head.left.left.right.left = new node(9);
        head.left.left.right.left.left = new node(10);
        head.right.right.left.right = new node(11);
        System.out.println("Nodes 2 and 3 are siblings : " + isCousin(head, 2, 3));
        System.out.println("Nodes 6 and 10 are siblings : " + isCousin(head, 6, 10));
        System.out.println("Nodes 7 and 8 are siblings : " + isCousin(head, 7, 8));

    }
}