Objective: Two numbers represented by a linked listwhere each node contains single digit. The digits are stored in Forward order, means head is pointing to the last digit of the number.

Input: Two numbers represented by Linked Lists

Output: Addition of two numbers represented by a Linked List.

Example:

First Number : 1007
Second Number : 93
Addition : 1100

Two numbers represented by a linked list, Number Stored in FORWARD order

Approach:

Get the length of both the lists.

If lengths are not equal, make them equal by adding nodes with value 0 in front of shorter linked list.

Append 0 in front Shorter List

Create a global variable carry=0.

Create a newHead = null;

newHead will be the starting node of our result linked list and curr node will the reference to the current node on which we are working in our result linked list.

Now using recursion travel in both the list till the end.

So now nodes are stores in a stack

Now while coming back, each node will pop out from the stack in reverse order

Take node data from both the lists add them along with carry.

if sum is >=10 , then make carry as 1 and create a new node with sum-10

Else just create a new Node with sum.

Add the newly created node to the result linked list with the help of newHead.

Complete Code:

Output:

First Number : ->1->0->0->7
Second Number : ->9->3
Addition : ->1->1->0->0

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If you find anything incorrect or you feel that there is any better approach to solve the above problem, please write comment.
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Above solution gives wrong output for the inputs like below :

First Number : ->1->1->1->7
Second Number : ->9->9->9->9
Addition : ->1->1->1->6

There is no extra last carry bit added according to the existing code. Please modify the logic accordinglty

tutorialhorizon

Thanks a lot indra, i have corrected the code. Let me know if you see errors in this or other posts

Siddhi Mohite

Can I get the code/algorithm for adding two binary numbers using doubly linked lists in cpp?

biswajit singh

hey i think this can be done in a relatively easier manner using iterative method. we could maintain 2 queues and store elements of these linked lists in the queues. we could then pop these elements out and keep adding them to 2 different strings . after that we could convert these strings into integer and output the number in the form of a linked list. takes up extra space tho!