Java Program To Subtract Two Numbers Represented As Linked Lists

// Java program to subtract smaller valued
// list from larger valued list and return
// result as a list.
import java.util.*;
import java.lang.*;
import java.io.*;

class LinkedList 
{
    // Head of list
    static Node head; 
    boolean borrow;

    // Node Class 
    static class Node 
    {
        int data;
        Node next;

        // Constructor to create a 
        // new node
        Node(int d)
        {
            data = d;
            next = null;
        }
    }

    /* A utility function to get length 
       of linked list */
    int getLength(Node node)
    {
        int size = 0;
        while (node != null) 
        {
            node = node.next;
            size++;
        }
        return size;
    }

    /* A Utility that padds zeros in front 
       of the Node, with the given diff */
    Node paddZeros(Node sNode, int diff)
    {
        if (sNode == null)
            return null;

        Node zHead = new Node(0);
        diff--;
        Node temp = zHead;
        while ((diff--) != 0) 
        {
            temp.next = new Node(0);
            temp = temp.next;
        }
        temp.next = sNode;
        return zHead;
    }

    /* Subtract LinkedList Helper is a recursive
       function, move till the last Node, and 
       subtract the digits and create the Node 
       and return the Node. If d1 < d2, we borrow 
       the number from previous digit. */
    Node subtractLinkedListHelper(Node l1, 
                                  Node l2)
    {
        if (l1 == null && 
            l2 == null && borrow == false)
            return null;

        Node previous = subtractLinkedListHelper(
                        (l1 != null) ? l1.next: null,
                        (l2 != null) ? l2.next : null);

        int d1 = l1.data;
        int d2 = l2.data;
        int sub = 0;

        /* If you have given the value to 
           next digit then reduce the d1 by 1 */
        if (borrow) 
        {
            d1--;
            borrow = false;
        }

        /* If d1 < d2, then borrow the number 
           from previous digit. Add 10 to d1 
           and set borrow = true; */
        if (d1 < d2) 
        {
            borrow = true;
            d1 = d1 + 10;
        }

        // Subtract the digits 
        sub = d1 - d2;

        // Create a Node with sub value 
        Node current = new Node(sub);

        // Set the Next pointer as Previous 
        current.next = previous;

        return current;
    }

    /* This API subtracts two linked lists 
       and returns the linked list which 
       shall have the subtracted result. */
    Node subtractLinkedList(Node l1, 
                            Node l2)
    {
        // Base Case.
        if (l1 == null && l2 == null)
            return null;

        // In either of the case, get the 
        // lengths of both Linked list.
        int len1 = getLength(l1);
        int len2 = getLength(l2);

        Node lNode = null, sNode = null;

        Node temp1 = l1;
        Node temp2 = l2;

        // If lengths differ, calculate the 
        // smaller Node and padd zeros for 
        // smaller Node and ensure both larger 
        // Node and smaller Node has equal length.
        if (len1 != len2) 
        {
            lNode = len1 > len2 ? l1 : l2;
            sNode = len1 > len2 ? l2 : l1;
            sNode = paddZeros(sNode, Math.abs(len1 - len2));
        }

        else {
            // If both list lengths are equal, then
            // calculate the larger and smaller list.
            // If 5-6-7 & 5-6-8 are linked list, then
            // walk through linked list at last Node
            // as 7 < 8, larger Node is 5-6-8 and
            // smaller Node is 5-6-7.
            while (l1 != null && l2 != null) 
            {
                if (l1.data != l2.data) 
                {
                    lNode = (l1.data > l2.data ? 
                             temp1 : temp2);
                    sNode = (l1.data > l2.data ? 
                             temp2 : temp1);
                    break;
                }
                l1 = l1.next;
                l2 = l2.next;
            }
        }

        // After calculating larger and smaller 
        // Node, call subtractLinkedListHelper 
        // which returns the subtracted linked list.
        borrow = false;
        return subtractLinkedListHelper(lNode, 
                                        sNode);
    }

    // Function to display the linked list
    static void printList(Node head)
    {
        Node temp = head;
        while (temp != null) 
        {
            System.out.print(temp.data + 
                             " ");
            temp = temp.next;
        }
    }

    // Driver code
    public static void main(String[] args)
    {
        Node head = new Node(1);
        head.next = new Node(0);
        head.next.next = new Node(0);
        Node head2 = new Node(1);
        LinkedList ob = new LinkedList();
        Node result = ob.subtractLinkedList(head, 
                                            head2);
        printList(result);
    }
}
// This article is contributed by Chhavi