solution.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution 
{
public:
    ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) 
    {
        ListNode *resultList = new ListNode(0);
        ListNode *tempNode = resultList;

        int tempSum = 0;
        int tempVal1;
        int tempVal2;
        int carry = 0;
        while(l1 != NULL || l2 != NULL)
        {
            if(l1 != NULL)
            {
                tempVal1 = l1->val;
                l1 = l1->next;
            }
            else
                tempVal1 = 0;

            if(l2 != NULL)
            {
                tempVal2 = l2->val;
                l2 = l2->next;
            }
            else
                tempVal2 = 0;

            tempSum = tempVal1 + tempVal2 + carry;
            tempNode->next = new ListNode(tempSum%10);
            carry = tempSum/10;
            tempNode = tempNode->next;
        }

        if(carry == 1)
            tempNode->next = new ListNode(1);

        return resultList->next;
    }
};