/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(-1);
        ListNode cur = dummy;
        int addon = 0;

        while (l1 != null && l2 != null){
            int sum = l1.val + l2.val + addon;
            ListNode newNode = new ListNode(sum % 10);
            addon = sum / 10;
            cur.next = newNode;
            cur = newNode;
            l1 = l1.next;
            l2 = l2.next;
        }

        while (l1 != null){
            int sum = l1.val + addon;
            ListNode newNode = new ListNode(sum % 10);
            addon = sum / 10;
            cur.next = newNode;
            cur = newNode;
            l1 = l1.next;
        }

        while (l2 != null){
            int sum = l2.val + addon;
            ListNode newNode = new ListNode(sum % 10);
            addon = sum / 10;
            cur.next = newNode;
            cur = newNode;
            l2 = l2.next;
        }

        if (addon > 0){
            ListNode newNode = new ListNode(addon);
            cur.next = newNode;
        }

        return dummy.next;
    }
}