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

Solution

/**
 * 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(0);
        int add = 0, v1, v2, v;
        ListNode *p1 = l1, *p2 = l2, *p = dummy;
        while ( p1 != NULL or p2 != NULL ) {
            if ( p1 == NULL ) v1 = 0;
            else {
                v1 = p1->val;
                p1 = p1->next;
            }
            if ( p2 == NULL ) v2 = 0;
            else {
                v2 = p2->val;
                p2 = p2->next;
            }
            v = (v1 + v2 + add)%10;
            add = (v1 + v2 + add)/10;
            p->next = new ListNode(v);
            p = p->next;
        }
        if ( add == 1 ) p->next = new ListNode(1);
        return dummy->next;
    }
};