public class Solution {
        public ListNode AddTwoNumbers(ListNode l1, ListNode l2)
        {
            ListNode start = null;
            ListNode currentNode = null;
            int remainder = 0;
            while ((l1 != null) || (l2 != null))
            {
                var sum = l1.val + l2.val + remainder;
                if(sum >= 10){
                    sum -= 10;
                    remainder = 1;
                }
                else {
                    remainder = 0;
                }
                l1 = l1.next;
                l2 = l2.next;

                if (currentNode == null)
                {
                    currentNode = new ListNode(sum);
                    start = currentNode;
                }
                else
                {
                    currentNode.next = new ListNode(sum);
                    currentNode = currentNode.next;
                }
            }
            return start;
        }
}-