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