1class Solution {2    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {3        ListNode dummy = new ListNode(0), tail = dummy;4        int carry = 0;5        while (l1 != null || l2 != null || carry != 0) {6            int sum = carry + (l1 == null ? 0 : l1.val) + (l2 == null ? 0 : l2.val);7            tail.next = new ListNode(sum % 10);8            tail = tail.next;9            carry = sum / 10;10            if (l1 != null) l1 = l1.next;11            if (l2 != null) l2 = l2.next;12        }13        return dummy.next;14    }15}