/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    /**
     * @param l1: the first list
     * @param l2: the second list
     * @return: the sum list of l1 and l2 
     */
    ListNode *addLists(ListNode *l1, ListNode *l2) {
        // write your code here
        ListNode *newhead = new ListNode(0);
        ListNode *p = newhead;
        int c = 0;
        while (l1 || l2 || c) {
            if (l1) {
                c += l1?l1->val:0;
                l1 = l1->next;
            }
            if (l2) {
                c += l2?l2->val:0;
                l2 = l2->next;
            }
            // p->val = c;
            p->next = new ListNode(c);
            c /= 10;
            p = p->next;
        }
        return newhead->next;
    }
};