using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        private static List<TournamentPlayer> ChoosePairs(IEnumerable<TournamentPlayer> players)

        {

            var matched = new List<TournamentPlayer>();

​

            List<TournamentPlayer> ordered = players

            .GroupBy((player) => player.TournamentPoints)  // Group by score

            .OrderBy((grp) => grp.Key)          // Sort groups (by score)

            .Select((grp) => grp.Shuffle())     // Shuffle players within each group

            .SelectMany((grp) => grp).ToList(); // Flatten groups back to single list

​

            if (tryMatchup(ordered, matched))

                return matched;

            else

                return null;

        }

​

        private static bool tryMatchup(List<TournamentPlayer> available, List<TournamentPlayer> matched)

        {

            if (available.Count == 0)

            {

                return true;

            }

​

            var player = available.First();

            available.Remove(player);

            matched.Add(player);

​

            var unmatched = available.Where(p => !player.Opponents.Contains(p)).ToList();

​

            foreach (var player2 in unmatched)

            {

                var pos = available.IndexOf(player2);

​

                available.Remove(player2);

                matched.Add(player2);

​

                if (tryMatchup(available, matched))

                {

                    return true;

                }

​

                matched.Remove(player2);

                available.Insert(pos, player2);

            }

​

            available.Insert(0, player);

            matched.Remove(player);

​

            return false;

        }

    }

}