using System;

using System.Collections.Generic;

using System.Linq;

​

public class OneHitWonders

{

    public static List<Song> DetermineOneHitWonders(List<Song> songs)

    {

        var songsByArtist = songs.GroupBy(song => song.Artist);

        var oneHitWonderGroups = songsByArtist.Where(songGroup => songGroup.Count() == 1);

        var oneHitWonders = oneHitWonderGroups.Select(songGroup => songGroup.ElementAt(0));

​

        return oneHitWonders.ToList();

    }

}

​

public class Song

{

    public int Id { get; set; }

    public string Name { get; set; }

    public string Artist { get; set; }

}

​

​

public class Program

{

    public static void Main()

    {

        var songs = new List<Song>

        {

            new Song { Id=1, Name="Foo", Artist="FooFighters" },

            new Song { Id=2, Name="TheOne", Artist="OneHitWonder" },

            new Song { Id=3, Name="Bar", Artist="FooFighters" },

            new Song { Id=4, Name="FooBar", Artist="FooFighters" }

        };

​

        var oneHitWonders = OneHitWonders.DetermineOneHitWonders(songs);

        var debugWonders = String.Join("\n", oneHitWonders.Select(song => $"{song.Id} {song.Name} {song.Artist}"));

        Console.WriteLine(debugWonders);

    }

}