AddTwoNumbers leetcode

SumTwoValues.cs

public class ListNodeSolution
    {
        public class ListNode
        {
            public int val;
            public ListNode next;
            public ListNode(int val = 0, ListNode next = null)
            {
                this.val = val;
                this.next = next;
            }
        }


        public ListNode SumTwoValues(ListNode list1, ListNode list2)
        {
            ListNode currentNode = null;
            ListNode head = null;

            int carry = 0;
            while (list1 != null || list2 != null)
            {
                int sum = GetSum(list1) + GetSum(list2) + carry;

                carry = sum / 10;

                int value = sum % 10;

                ListNode node = new ListNode(value);

                currentNode ??= head = node;
                currentNode.next = node;
                currentNode = currentNode.next;

                list1 = list1?.next;
                list2 = list2?.next;
            }

            return head;
        }
     
        public int GetSum(ListNode node)
        {
            return node?.val ?? 0;
        }
        static void Main(string[] args)
        {
            ListNodeSolution listNode = new ListNodeSolution();
            ListNode head1 = new ListNode();

            int[] numbers = new[] { 47, 56, 127, 963, 47, 15, 98, 32, 1 };

            //head1.FindIndexRecursiveHelper(numbers, 1111, 8);

            //head1.FindIndex_Recursive(numbers, 1, 8);

            head1 = new ListNode(9);
            head1.next = new ListNode(9);
            head1.next.next = new ListNode(9);
            head1.next.next.next = new ListNode(9);
            head1.next.next.next.next = new ListNode(9);
            head1.next.next.next.next.next = new ListNode(9);
            head1.next.next.next.next.next.next = new ListNode(9);
            Console.Write("First list is ");


            ListNode head2 = new ListNode();

            head2 = new ListNode(9);
            head2.next = new ListNode(9);
            head2.next.next = new ListNode(9);
            head2.next.next.next = new ListNode(9);
            Console.Write("Second list is ");

            listNode.SumTwoValues(head1, head2);

            Console.ReadLine();
        }
    }