[Leetcode] 2. Add Two Numbers QuestionEditorial Solution

        public static ListNode AddTwoNumbers(ListNode l1, ListNode l2)
        {
              ListNode ret = new ListNode(0);
            ListNode cur = ret;

            int sum = 0;
            while (true)
            {
                if (l1 != null)
                {
                    sum += l1.val;
                    l1 = l1.next;
                }

                if (l2 != null)
                {
                    sum += l2.val;
                    l2 = l2.next;
                }

                cur.val = sum % 10;

                sum /= 10;

                if (l1 != null || l2 != null || sum != 0)
                {
                    cur = (cur.next = new ListNode(0));
                }
                else
                    break;
            }

            return ret;
        }