[LeetCode #2] Add Two Numbers

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

class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode dummy(0);
        ListNode *p = &dummy;
        ListNode *p1 = l1, *p2 = l2;
        
        int carry = 0;
        
        while (p1 || p2){
            int n1 = p1 ? p1->val : 0;
            int n2 = p2 ? p2->val : 0;
            int sum = n1 + n2 + carry;
            carry = sum / 10;
            p->next = new ListNode(sum % 10);
            p = p->next;
            if (p1) p1 = p1->next;
            if (p2) p2 = p2->next;
        }
        
        if (carry){
            p->next = new ListNode(carry);
        }
        
        return dummy.next;
    }
};