LinkedList.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;

namespace NewProject
{
    internal class LinkedList
    {

        public class LinkedListNode
        {
            public LinkedListNode Next;
            public LinkedListNode Prev;

        }
        public LinkedListNode First;
        public LinkedListNode Last;
        public string Type;

        public LinkedListNode Next(LinkedListNode node)
        {
            return node.Next;
        }
        public LinkedListNode Prev(LinkedListNode node)
        {
            return node.Prev;
        }
        public LinkedListNode Insert(LinkedListNode prevNode)
        {
            var newNode = new LinkedListNode();

            if (First == null)
            {
                First = Last = newNode;
            }
            else if (prevNode.Next == null)
            {
                newNode.Prev = prevNode;
                prevNode.Next = newNode;
                Last = newNode;
            }
            else if (prevNode.Next != null)
            {
                prevNode.Next.Prev = newNode;
                newNode.Next = prevNode.Next;
                newNode.Prev = prevNode;
                prevNode.Next = newNode;

            }
            return newNode;
        }

    }

}