using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main(string[] args)

    {

        var mastermind = new Mastermind(new List<CodePeg> { CodePeg.Black, CodePeg.Blue, CodePeg.Yellow, CodePeg.Blue });

        var hints = mastermind.GetHints(new List<CodePeg> { CodePeg.Black, CodePeg.Blue, CodePeg.Green, CodePeg.Yellow });

        foreach (var hint in hints)

        {

            Console.WriteLine(hint);

        }

    }

}

​

public class Mastermind

{

    private List<CodePeg> code;

    private HashSet<Movement> movements;

    private HashSet<CodePeg> pegs;

​

    public Mastermind(List<CodePeg> code)

    {

        this.code = code;

        // precalculate all the movements

        this.movements = code.Select((peg, position) => new Movement { Position = position, Peg = peg }).ToHashSet();

        // precalculate all the pegs

        this.pegs = code.ToHashSet();

    }

​

    public List<ResultPeg> GetHints(List<CodePeg> guess)

    {

        // separate the results in black and white to define priority

        var blacks = new List<ResultPeg>();

        var whites = new List<ResultPeg>();

        for (var i = 0; i < guess.Count; i++)

        {

            var position = i;

            var peg = guess[i];

            var movement = new Movement { Position = position, Peg = peg };

            if (movements.Contains(movement))

            {

                // first priority, match by position and color

                blacks.Add(ResultPeg.Black);

            }

            else if (pegs.Contains(peg))

            {

                // second priority, match by color

                whites.Add(ResultPeg.White);

            }

        }

        // Only take 4 as maximum entries. Prioritizin the blacks (correct position and correct color)

        return blacks.Concat(whites).Take(4).ToList();

    }

}

​

public enum CodePeg

{

    Black,

    Blue,

    Green,

    Red,

    White,

    Yellow,

}

​

public enum ResultPeg

{

    Black,

    White,

}

​

public class Movement : IEquatable<Movement>

{

    public int Position { get; set; }

    public CodePeg Peg { get; set; }

    public bool Equals(Movement other)

    {

        return other != null && Position == other.Position && Peg == other.Peg;

    }

    public override bool Equals(Object obj)

    {

        return Equals(obj as Movement);

    }

    public override int GetHashCode()

    {

        return Position.GetHashCode() ^ Peg.GetHashCode();

    }

}