leetcode 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 = new ListNode(0);
        ListNode* p = head;
        int carry = 0;
        while(true) {
            if(l1 != NULL) {
                carry += l1->val;
                l1 = l1->next;
            }
            if(l2 != NULL) {
                carry += l2->val;
                l2 = l2->next;
            }
            p->val = carry % 10;
            carry /= 10;
            if(l1 != NULL || l2 != NULL || carry != 0) {
                p->next = new ListNode(0);
                p = p->next;
            }else {
                break;
            }
        }
        return head;
    }
};