/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        auto dummy = new ListNode(), cur = dummy;
        int carry = 0;
        while(l2 || l1 || carry) {
            if(l1) carry += l1->val, l1 = l1->next;
            if(l2) carry += l2->val, l2 = l2->next;
            cur->next = new ListNode(carry % 10);
            cur = cur->next;
            carry /= 10;
        }
        return dummy->next;
    }
};