using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    // https://bowlingguidance.com/all-about-strikes-and-spares-in-bowling/

    static int Score(IList<int> pins)

    {

        bool startsWithStrike(IList<int> xs) => xs[0] == 10;

        bool startsWithSpare(IList<int> xs) => xs[0] + xs[1] == 10;

        int Loop(int accumulator, int turn, IList<int> list)

        {

            //Console.WriteLine($"{turn}: {accumulator}");

            if (turn == 0)

            {

                return accumulator;

            }

​

            if (startsWithStrike(list))

            {

                return Loop(10 + list[1] + list[2] + accumulator, turn - 1, list.SkipList(1));

            }

​

            if (startsWithSpare(list))

            {

                return Loop(10 + list[2] + accumulator, turn - 1, list.SkipList(2));

            }

​

            return Loop(list[0] + list[1] + accumulator, turn - 1, list.SkipList(2));

        }

​

        return Loop(0, 10, pins);

    }

​

    public static void Main()

    {

        var zeros = Enumerable.Repeat(0, 20).ToList();

        Console.WriteLine(Score(zeros) == 0);

        var zerosAndOne = Enumerable.Repeat(0, 19).Prepend(1).ToList();

        Console.WriteLine(Score(zerosAndOne) == 1);

        var zerosAndStrike = Enumerable.Repeat(0, 19).Prepend(10).ToList();

        Console.WriteLine(Score(zerosAndStrike) == 10);

        var strikes = Enumerable.Repeat(10, 12).ToList();

        Console.WriteLine(Score(strikes) == 300);

        var zerosAndSpare = Enumerable.Repeat(0, 18).Prepend(9).Prepend(1).ToList();

        Console.WriteLine(Score(zerosAndSpare) == 10);

        var spares = Enumerable.Repeat(new []{9, 1}, 10).SelectMany(x => x).Append(9).ToList();

        Console.WriteLine(Score(spares) == 190);

    }

}

​

public static class Extensions

{

    public static IList<T> SkipList<T>(this IList<T> list, int n) => list.Skip(n).ToList();

}