```
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
if (l1 == null)
return l2;
if (l2 == null)
return l1;
ListNode head = new ListNode(0), r = head, p = l1, q = l2, tmp;
r.next = null;
int carry = 0, sum;
while (p != null || q != null) {
sum = 0;
sum += carry;
if (p != null) {
sum += p.val;
p = p.next;
}
if (q != null) {
sum += q.val;
q = q.next;
}
tmp = new ListNode(sum % 10);
carry = sum / 10;
r.next = tmp;
r = r.next;
}
if (carry == 1) {
tmp = new ListNode(1);
r.next = tmp;
r = r.next;
}
r.next = null;
return head.next;
}
```