Add Two Numbers

http://oj.leetcode.com/problems/add-two-numbers/

Note:

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

/**
 * 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 dummy(0);
        ListNode *cur = &dummy;
        int carry = 0;
        while (l1 || l2 || carry) {
            int sum = carry;
            if (l1) {
                sum += l1->val;
                l1 = l1->next;
            }
            if (l2) {
                sum += l2->val;
                l2 = l2->next;
            }
            carry = sum / 10;
            sum %= 10;
            ListNode *node = new ListNode(sum);
            cur->next = node;
            cur = cur->next;
        }
        return dummy.next;
    }
};