using System;

​

public class Program

{

    public static void Main()

    {

        var list = new LinkedList.ListNode(4)

        {Next = new LinkedList.ListNode(5)

        {Next = new LinkedList.ListNode(6)

        {Next = new LinkedList.ListNode(1)

        {Next = new LinkedList.ListNode(2)

        {Next = new LinkedList.ListNode(4)}}}}};

        LinkedList linkedList = new LinkedList();

        linkedList.HeadNode = list;

        linkedList.Display();

        var result = linkedList.PairReverce(list);

        linkedList.HeadNode = result;

        linkedList.Display();

    }

}

​

/// <summary>

/// Односвязанный список

/// </summary>

public class LinkedList

{

    /// <summary>

    /// Главный узел

    /// </summary>

    public ListNode HeadNode

    {

        get;

        set;

    }

​

    public ListNode PrevNode

    {

        get;

        set;

    }

​

    public ListNode FistNode;

    public ListNode SecondNode;

    /// <summary>

    /// Узел

    /// </summary>

    public class ListNode

    {

        /// <summary>

        /// Значение узла

        /// </summary>

        public int Value;

        /// <summary>

        /// Ссылка на следующий узел

        /// </summary>

        public ListNode Next;

        /// <summary>

        /// Ссылка на последний узел

        /// </summary>

        public ListNode Tail;

        /// <summary>

        /// Конструктор по умолчанию

        /// </summary>

        /// <param name = "value">значение</param>

        public ListNode(int value)

        {

            this.Value = value;

            this.Next = null;

        }

    }

​

    public ListNode PairReverce(ListNode head)

    {

        var firstNode = head;

        var secondNode = head.Next;

        head = secondNode;

        while (true)

        {

            var next = secondNode.Next;

            secondNode.Next = firstNode;

            if (next == null || next.Next == null)

            {

                firstNode.Next = next;

                break; // если больше нет пар, выходим из цикла

            }

​

            firstNode.Next = next.Next;

            firstNode = next;

            secondNode = firstNode.Next;

        }

​

        return head;

    }

​

    /// <summary>

    /// Вывести односвязанный список

    /// </summary>

    public void Display()

    {

        Console.WriteLine();

        ListNode currentListNode = HeadNode;

        while (currentListNode != null)

        {

            Console.Write("{0} ", currentListNode.Value);

            currentListNode = currentListNode.Next;

        }

    }

}