AddTwoNumbersasLists.cpp

/*
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

    342 + 465 = 807
Make sure there are no trailing zeros in the output list
So, 7 -> 0 -> 8 -> 0 is not a valid response even though the value is still 807.

LINK: https://www.interviewbit.com/problems/add-two-numbers-as-lists/
*/

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
ListNode* Solution::addTwoNumbers(ListNode* A, ListNode* B)
{
    if(A==NULL)
        return B;
    if(B==NULL)
        return A;
 
    ListNode *head = new ListNode(0);
    ListNode *temp = head;
    int carry = 0;
 
    while(A || B)
    {
        int sum = carry;
 
        if(A)
        {
            sum += A->val;
            A = A->next;
        }
        if(B)
        {
            sum += B->val;
            B = B->next;
        }
 
        carry = sum/10;
        sum %= 10;
        temp->val = sum;
        if(A || B)
        {
            temp->next = new ListNode(0);
            temp = temp->next;
        }
    }
 
    if(carry)
    {
        temp->next = new ListNode(0);
        temp = temp->next;
        temp->val = carry;
    }
 
    return head;
}