using System;

public class Program

{

    public static void Main()

    {

        var p = new Program();

        var node4 = new ListNode(100000, null);

        var node3 = new ListNode(3, node4);

        var node2 = new ListNode(3, node3);

        var node1 = new ListNode(3, node2);

        var node0 = new ListNode(-8, node1);

        p.DeleteDuplicates(node0);

        node0.Print();

    }

    public ListNode DeleteDuplicates(ListNode head) {

        if (head is null) {

            return null;

        }

        ListNode currentNode = head;

        while (currentNode.next is {}) {

            if (currentNode.val == currentNode.next.val) {

                // delete next node

                DeleteNode(currentNode, currentNode.next);

            } else {

                currentNode = currentNode.next;

            }

​

        }

        return head;

    }

    public bool DeleteNode(ListNode prevNode, ListNode nodeToDelete) {

        prevNode.next = nodeToDelete.next;

        nodeToDelete = null;

        return true;

    }

}

​

public class ListNode {

    public int val;

    public ListNode next;

    public ListNode(int val=0, ListNode next=null) {

        this.val = val;

        this.next = next;

    }

    public void Print() {

        ListNode currentNode = this;

        Console.Write($"{currentNode.val}");

        while (currentNode.next is {}) {

            currentNode = currentNode.next;

            Console.Write($" -> {currentNode.val}");

        }

    }

}