distance BT java

// http://code2begin.blogspot.com
// program to find distance between 2 nodes in a given binary tree

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

import java.io.*;
import java.lang.reflect.Array;
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 find the least common ancestor of 2 nodes in a binary tree
    static node least_common_ancestor(node root, int n1, int n2){
        if(root == null){
            return root;
        }

        if(root.data == n1 || root.data == n2){
            return root;
        }

        node left = least_common_ancestor(root.left, n1, n2);
        node right = least_common_ancestor(root.right, n1, n2);

        if(left != null && right != null){
            return root;
        }

        if(left != null){
            return least_common_ancestor(root.left, n1, n2);
        }
        return least_common_ancestor(root.right, n1, n2);
    }


    // function that returns the distance between 2 given nodes
    static int distance_between(node root, int a, int b){
        node LCA = least_common_ancestor(root, a, b);
        return level_of_node(LCA, a) + level_of_node(LCA, b);
    }



    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("Distance between nodes 6 and 10 is : " + distance_between(head, 6, 10));
        System.out.println("Distance between nodes 1 and 10 is : " + distance_between(head, 1, 10));
        System.out.println("Distance between nodes 11 and 10 is : " + distance_between(head, 11, 10));

    }
}