/// <summary>

    /// 节点

    /// </summary>

    /// <typeparam name="T"></typeparam>

    public class LinkedListNode<T>

    {

        public LinkedListNode(T value)

        {

            this.Value = value;

        }

        public T Value { get; private set; }//值

        /// <summary>

        /// 后一个节点

        /// </summary>

        public LinkedListNode<T> Next { get; internal set; }

        /// <summary>

        /// 前一个节点

        /// </summary>

        public LinkedListNode<T> Prev { get; internal set; }

    }

 public class LinkedList<T> : IEnumerable<T>

    {

        public LinkedListNode<T> First { get; private set; }

        public LinkedListNode<T> Last { get; private set; }

        public LinkedListNode<T> AddLast(T node)

        {

            var newNode = new LinkedListNode<T>(node);

            if(First == null)

            {

                First = newNode;

                Last = First;

            }

            else

            {

                LinkedListNode<T> previous = Last;

                Last.Next = newNode;

                Last = newNode;

                Last.Prev = previous;

            }

            return newNode;

        }

        public IEnumerator<T> GetEnumerator()

        {

            LinkedListNode<T> current = First;

            while (current!=null)

            {

                yield return current.Value;

                current = current.Next;

            }

        }

        IEnumerator IEnumerable.GetEnumerator()

        {

            return GetEnumerator();

        }

    }

 static void Main(string[] args)

        {

            try

            {

                Console.WriteLine("**********************LinkedList<int>*********************");

                var list1 = new LinkedList<int>();

                list1.AddLast();

                list1.AddLast();

                list1.AddLast();

                list1.AddLast();

                foreach (var item in list1)

                {

                    Console.WriteLine(item);

                }

                Console.WriteLine("*********************LinkedList<string>**********************");

                var list2 = new LinkedList<string>();

                list2.AddLast("");

                list2.AddLast("aaaa");

                list2.AddLast("bbbbb");

                list2.AddLast("cccc");

                foreach (var item in list2)

                {

                    Console.WriteLine(item);

                }

            }

            catch (Exception ex)

            {

                Console.WriteLine("程序出现错误：" + ex.Message);

            }

            Console.ReadKey();

        }