using System;

​

public class Program

{

    public static void Main()

    {

        var first = new Node(1);

        first.Push(2).Push(3).Push(4).Push(5).Push(6).Push(7).Push(8).Push(9).Push(10);

        first.Print();

        var sorted = ReverseAlternateInGroup(first, 3);

        Console.WriteLine("=============== After reversing ===============");

        sorted.Print();

    }

​

    static Node ReverseAlternateInGroup(Node node, int group)

    {

        var current = node;

        Node next = null, prev = null;

        int count = 0;

        while (count < group && current != null)

        {

            next = current.Next;

            current.Next = prev;

            prev = current;

            current = next;

            count++;

        }

​

        if (node != null)

        {

            node.Next = current;

        }

​

        count = 0;

        while (count < group - 1 && current != null)

        {

            current = current.Next;

            count++;

        }

​

        if (current != null)

        {

            current.Next = ReverseAlternateInGroup(current.Next, group);

        }

​

        return prev;

    }

}

​

public class Node

{

    public int Data

    {

        get;

        set;

    }

​

    public Node Next

    {

        get;

        set;

    }

​

    public Node(int data)

    {

        Data = data;

        Next = null;

    }

​

    public void Print()

    {

        var node = this;

        do

        {

            Console.Write(node.Data + " ");

            node = node.Next;

        }

        while (node != null);

        Console.WriteLine();

    }

​

    public int GetLengthIterative()

    {

        var node = this;

        var count = 0;

        while (node != null)

        {

            count++;

            node = node.Next;

        }

​

        return count;

    }

​

    public int GetLengthRecursive()

    {

        if (Next == null)

        {

            return 1;

        }

​

        return 1 + Next.GetLengthRecursive();

    }

​

    public Node Push(int data)

    {

        var node = new Node(data);

        Next = node;

        return node;

    }

​

    public override string ToString()

    {

        return Data.ToString();

    }

}