Bulls and Cows

using System;
using System.Collections.Generic;
using System.Linq;


// namespace:   bullsandcows
//
// summary:	    A challenge made by the forum "FXP", 
//              to build a quick game of "bulls and cows" 
//              in a short time.
//              Entry creator: CC_CC

namespace bullsandcows
{
    /// <summary>   A static class to provide assistant functions over generic type. </summary>
    public static class Applier
    {
        /// <summary>   Applies a function over argument. </summary>
        ///
        /// <typeparam name="TIn">  Type of the argument for application. </typeparam>
        /// <typeparam name="TOut"> Type of the applied argument result. </typeparam>
        /// <param name="x">    The applied argument. </param>
        /// <param name="f">    The function applied over the argument. </param>
        ///
        /// <returns>   The applied argument result. </returns>
        public static TOut Apply<TIn, TOut>(this TIn x, Func<TIn, TOut> f) => f(x);
    }

    /// <summary>   The program main class. </summary>
    class Program
    {
        /// <summary>   Returns how many values are similar
        ///             in the same position in guess and gen,
        ///             and in different position in guess and gen. </summary>
        ///
        /// <exception cref="ArgumentException">    Thrown when guess or gen 
        ///                                         aren't the same length. </exception>
        ///
        /// <typeparam name="T">    Type of argument to compare guess and gen. </typeparam>
        /// <param name="guess">    The guessed input. </param>
        /// <param name="gen">      The generated value. </param>
        ///
        /// <returns>   First result number of similar values in the same position,
        ///             Second result number of similar values in different position. </returns>
        private static (int, int) Score<T>(IEnumerable<T> guess, IEnumerable<T> gen) where T : IEquatable<T>
        {
            var (bulls, nonbulls) = guess.Zip(gen)
                .ToLookup(x =>
                {
                    if (x.First == null || x.Second == null)
                        throw new System.ArgumentException("guess and gen aren't the same length");
                    return x.First.Equals(x.Second);
                })
                .Apply(x => (x[true], x[false]));

            var cows = nonbulls
                .Apply(x => (x.Select(xs => xs.First),
                            x.Select(xs => xs.Second)))
                .Apply(x => x.Item1.Intersect(x.Item2));

            return (bulls.Count(), cows.Count());
        }

        /// <summary>   Main entry-point for this application. </summary>
        public static void Main()
        {
            var nTry = 0;
            var bulls = 0;
            var cows = 0;
            var rand = new Random(Guid.NewGuid().GetHashCode());

            Console.WriteLine("Enter the length of the number you intending to guess");

            var length = int.Parse(Console.ReadLine());
            var gen = new char[length];

            for (int i = 0; i < gen.Length; i++)
                gen[i] = (char)rand.Next('0', '9');


            while (bulls != length)
            {
                Console.Write(nTry + ": ");
                var guess = Console.ReadLine().ToCharArray();
                if (guess.Length == length)
                {
                    (bulls, cows) = Score(guess, gen);
                    Console.WriteLine("Bulls={0}, Cows={1}", bulls, cows);
                    nTry++;
                }
                else
                    Console.WriteLine("Wrong length");
            }

            Console.WriteLine("you Win! tries: {0}", nTry);
        }
    }
}