002_add two numbers

/**
 * 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 head(0);
        ListNode* p = &head;
        int extra = 0;
        while(l1 || l2 || extra)
        {
            int sum = (l1 ? l1->val : 0) + (l2 ? l2->val : 0) + extra;
            extra = sum / 10;
            p->next = new ListNode(sum % 10);
            p = p->next;
            l1 = l1 ? l1->next : 0;
            l2 = l2 ? l2->next : 0;
        }
        
        return head.next;
    }
};