using System;

using System.Collections.Generic;

​

public abstract class PatternPrinter

{

    private int patternLength;

    public PatternPrinter(int patternLength)

    {

        this.patternLength = patternLength;

    }

​

    public void Print()

    {

        Random rnd = new Random();

        int specialIndex = rnd.Next(patternLength);

        for (int i = 0; i < patternLength; i++)

        {

            if (i == specialIndex)

                PrintSpecial();

            else

            {

                int roll = rnd.Next(2); // either 0 or 1

                if (roll == 0)

                    PrintNormal();

                else

                    PrintVariant();

            }

        }

    }

    public abstract void PrintNormal();

    public abstract void PrintVariant();

    public abstract void PrintSpecial();

​

}

​

public class RiverPattern : PatternPrinter

{

    public RiverPattern(int patternLength): base (patternLength)

    {

    }

​

    public override void PrintNormal()

    {

        for(int i = 0; i < 4; i++){

        Console.WriteLine("***O  O***\n");

        }

    }

​

    public override void PrintVariant()

    {

        Console.WriteLine("**O  O****\n");

        Console.WriteLine("*O  O*****\n");

        Console.WriteLine("**O  O****\n");

        Console.WriteLine("***O  O***\n");

    }

​

    public override void PrintSpecial()

    {

        Console.WriteLine("**O   O***\n");

        Console.WriteLine("*O     O**\n");

        Console.WriteLine("*O  OO  O*\n");

        Console.WriteLine("*O  O   O*\n");

        Console.WriteLine("**O    O**\n");

    }

}

​

public class Program

{

    public static void Main()

    {

        RiverPattern river = new RiverPattern(10);

        river.Print();

    }

}