na982

/**
 * 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 = new ListNode(-1);
        
        ListNode* target = dummy;
        int carry = 0;
        while(l1 || l2 || carry) {
            int l1_val = (l1) ? (l1->val) : (0);
            int l2_val = (l2) ? (l2->val) : (0);
            int sum = (l1_val + l2_val + carry);
            target->next = new ListNode(sum % 10);
            carry = sum / 10;
            
            target = target->next;
            l1 = (l1) ? (l1->next) : (l1);
            l2 = (l2) ? (l2->next) : (l2);
        }
        
        return dummy->next;
    }
};