Deque

using System;
using System.Collections.Generic;
using System.Collections;

namespace Deque
{
    internal class Program
    {
        static void Main(string[] args)
        {
            Deque<string> deque = new Deque<string>();
            deque.AddFirst("alice");
            deque.AddLast("kate");
            deque.AddLast("tom");
            foreach(string item in deque)
            {
                Console.WriteLine(item);
            }
            string removedItem = deque.RemoveFirst();
            Console.WriteLine($"\n удален: {removedItem}\n");
            foreach(string item in deque)
            {
                Console.WriteLine(item);
            }
        }
        public class DoublyNode<T>
        {
            public DoublyNode(T data)
            {
                Data = data;
            }
            public T Data { get; set; }
            public DoublyNode<T> Next { get; set; }
            public DoublyNode<T> Previous { get; set; }
        }
        public class Deque<T> : IEnumerable<T>//двухсязный список
        {
            DoublyNode<T> head;
            DoublyNode<T> tail;
            int count;

            //добавление элемента
            public void AddLast(T data)
            {
                DoublyNode<T> node = new DoublyNode<T>(data);
                if(head == null)
                {
                    head = node;
                }
                else
                {
                    tail.Next = node;
                    node.Previous = tail;
                }
                tail = node;
                count++;
            }
            public void AddFirst(T data)
            {
                DoublyNode<T> node = new DoublyNode<T>(data);
                DoublyNode<T> temp = head;
                node.Next = temp;
                head = node;
                if(count == 0)
                {
                    tail = head;
                }
                else
                {
                    temp.Previous = node;
                }
                count++;
            }
            public T RemoveFirst()
            {
                if(count == 0)
                {
                    throw new InvalidOperationException();
                }
                T output = head.Data;
                if(count == 1)
                {
                    head = tail = null;
                }
                else
                {
                    head = head.Next;
                    head.Previous = null;
                }
                count--;
                return output;
            }
            public T RemoveLast()
            {
                if(count == 0)
                {
                    throw new InvalidOperationException ();
                }
                T output = tail.Data;
                if (count == 1)
                {
                    head = tail = null;
                }
                else
                {
                    tail = tail.Previous;
                    tail.Next = null;
                }
                count--;
                return output;
            }
            public T First
            {
                get
                {
                    if(IsEmpty)
                    {
                        throw new InvalidOperationException();
                    }
                    return tail.Data;
                }
            }
            public int Count { get { return count; } }
            public bool IsEmpty { get { return count == 0; } }
            public void Clear()
            {
                head = tail = null;
                count = 0;
            }
            public bool Contains (T data)
            {
                DoublyNode<T> current = head;
                while(current != null)
                {
                    if(current.Data.Equals(data))
                    {
                        return true;
                    }
                    current = current.Next;
                }
                return false;
            }
            IEnumerator IEnumerable.GetEnumerator()
            {
                return ((IEnumerable)this).GetEnumerator();
            }
            IEnumerator<T> IEnumerable<T>.GetEnumerator()
            {
                DoublyNode<T> current = head;
                while(current != null)
                {
                    yield return current.Data;
                    current = current.Next;
                }
            }
        }
    }
}