```
public class Solution {
private ListNode reverse(ListNode node) {
ListNode prev = null, temp = null;
while (node != null) {
temp = node.next;
node.next = prev;
prev = node;
node = temp;
}
return prev;
}
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
l1 = reverse(l1);
l2 = reverse(l2);
int carry = 0;
ListNode dummy = new ListNode(0);
ListNode cur = dummy;
while (l1 != null || l2 != null || carry != 0) {
int sum = (l1 == null ? 0 : l1.val) + (l2 == null ? 0 : l2.val) + carry;
cur.next = new ListNode(sum % 10);
carry = sum / 10;
cur = cur.next;
l1 = l1 == null ? l1 : l1.next;
l2 = l2 == null ? l2 : l2.next;
}
return reverse(dummy.next);
}
}
```