Javascript Program To Subtract Two Numbers Represented As Linked Lists

Given two linked lists that represent two large positive numbers. Subtract the smaller number from the larger one and return the difference as a linked list. Note that the input lists may be in any order, but we always need to subtract smaller from the larger ones.
It may be assumed that there are no extra leading zeros in input lists.
Examples:

Input: l1 = 1 -> 0 -> 0 -> NULL,  l2 = 1 -> NULL
Output: 0->9->9->NULL
Explanation: Number represented as 
lists are 100 and 1, so 100 - 1 is 099

Input: l1 = 7-> 8 -> 6 -> NULL,  l2 = 7 -> 8 -> 9 NULL
Output: 3->NULL
Explanation: Number represented as 
lists are 786 and  789, so 789 - 786 is 3, 
as the smaller value is subtracted from 
the larger one.

Approach: Following are the steps.

1. Calculate sizes of given two linked lists.
2. If sizes are not the same, then append zeros in the smaller linked list.
3. If the size is the same, then follow the below steps:
   1. Find the smaller valued linked list.
   2. One by one subtract nodes of the smaller-sized linked list from the larger size. Keep track of borrow while subtracting.

Following is the implementation of the above approach.

Javascript

<script>
// Javascript program to subtract smaller
// valued list from larger valued list
// and return result as a list.

// head of list
var head;
var borrow;

// Node Class
class Node
{
    // Constructor to create a
    // new node
    constructor(d)
    {
        this.data = d;
        this.next = null;
    }
}

/* A utility function to get length
   of linked list */
function getLength(node)
{
    var 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 */
function paddZeros(sNode, diff)
{
    if (sNode == null)
        return null;

    var zHead = new Node(0);
    diff--;
    var 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. */
function subtractLinkedListHelper(l1,  l2)
{
    if (l1 == null && l2 == null &&
        borrow == false)
        return null;

    var previous =
        subtractLinkedListHelper((l1 != null) ?
                                  l1.next : null,
                                 (l2 != null) ?
                                  l2.next : null);
    var d1 = l1.data;
    var d2 = l2.data;
    var sub = 0;

    /* if you have given the value 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
    var 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. */
function subtractLinkedList(l1,  l2)
{
    // Base Case.
    if (l1 == null && l2 == null)
        return null;

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

    var lNode = null, sNode = null;
    var temp1 = l1;
    var 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
function printList(head)
{
    var temp = head;
    while (temp != null)
    {
        document.write(temp.data + " ");
        temp = temp.next;
    }
}

// Driver code
var head = new Node(1);
head.next = new Node(0);
head.next.next = new Node(0);
var head2 = new Node(1);
var result = subtractLinkedList(head,
                                head2);
printList(result);
// This code contributed by aashish1995
</script>

Output:

0 9 9 

Complexity Analysis:

• Time complexity: O(n). 
  As no nested traversal of linked list is needed.
• Auxiliary Space: O(n). 
  If recursive stack space is taken into consideration O(n) space is needed.

Please refer complete article on Subtract Two Numbers represented as Linked Lists for more details!