Addition in Linked List

Problem Statement

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

Solution

[sourcecode language="cpp"]

class Solution {
public:
ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {

if( l1 == NULL )
return l2;
if( l2 == NULL )
return l1;

int carry = 0;
ListNode *rider = l1, *prev = NULL;

while( rider != NULL && l2 != NULL )
{
int temp = rider->val + l2->val + carry;

rider->val = temp%10;
carry = temp/10;
prev = rider;

rider = rider->next;
l2 = l2->next;
}
if( rider == NULL && l2 == NULL )
{
if(carry > 0)
prev->next = new ListNode(carry);
}
else if( l2 == NULL )
{
while( carry > 0 && rider != NULL)
{
int temp = rider->val + carry;
rider->val = temp%10;
carry = temp/10;

prev = rider;
rider = rider->next;
}
if(carry > 0 && rider == NULL)
prev->next = new ListNode(carry);
}
else if( rider == NULL )
{
while( l2 != NULL )
{
int temp = l2->val + carry;
prev->next = new ListNode( temp%10 );

carry = temp/10;
prev = prev->next;
l2 = l2->next;
}
if( carry > 0)
prev->next = new ListNode( carry );
}

return l1;
}
};
[/sourcecode]