what a stupid question - here's a nasty hack 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* ll1=l1;
ListNode* last_l1;
int carryover=0;
while(l1)
{
int n=l1->val + (l2?l2->val:0) + carryover;
l1->val = n %10;
carryover = n/10;
if(!l1->next && l2)
{
l1->next=l2->next;
l2=nullptr;
}
last_l1=l1;
l1=l1->next;
l2=l2?l2->next:nullptr;
}
if(carryover)
last_l1->next = new ListNode(carryover);
return ll1;
}
};
```