using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Simple Round Robin Generator");

        Console.WriteLine("Ref: https://stackoverflow.com/q/77730901/1690217");

        // simulate setting X players in the UI

        Players = 6;

        Console.WriteLine($"{Players} Players");

        Console.WriteLine();

        // direct call to the event handler

        button_G_Click(null, EventArgs.Empty);

    }

    public static int Players { get;set; }

     private static void button_G_Click(object sender, EventArgs e)

     {

         int players = Players;

         int StartFrom = players % 2 == 0 ? 1 : 0; // if odd players, start from 0

         players = players % 2 == 0 ? players : players + 1; // if odd players, make even (with the help of the dummy)

         int Rounds = players - 1;

         int Game = 0;

​

         List<Pair> pairs = new List<Pair>();

​

         int TotalPairs = 0;

         List<int> WasPairedThisRound = new();

         bool ContainsPair(int player1, int player2)

         {

             foreach (Pair pair in pairs)

             {

                 if ((pair.Player1 == player1 && pair.Player2 == player2) ||

                     (pair.Player1 == player2 && pair.Player2 == player1))

                 {

                     return true;

                 }

​

             }

             return false;

         }

​

         // By complete the square, I mean to make the number of player matchups close to equal, the output should look like a square

         // So for 8, this needs 6

         // for 10, 3 is about as good as it gets

         // for 12, 2

         // Play with this if you want... 

         //int completeTheSquare = 2 * (int)Math.Round(Math.Sqrt(players),0) + 2;

         // 2 it turns out is not a bad general number for evens, 3 for odds

         int completeTheSquare = players % 2 == 0 ? 2 : 3;

​

         for (int round = 0; round < Rounds; round++)

         {

             //for (int player1 = StartFrom; player1 <= players; player1++)

             foreach (var p1 in Enumerable.Range(1,players))

             {

                 int startFrom = (p1 + round/completeTheSquare) % players;

                 if(StartFrom == 1) startFrom ++;

                 int player1 = startFrom;                

                 if (WasPairedThisRound.Count == players) { break; }

                 //for (int player2 = startFrom; player2 <= players; player2++)

                 foreach (var p2 in Enumerable.Range(1,players))

                 {

                     int player2 = (p2 + ((round/completeTheSquare)*3)) % players;

                     if(StartFrom == 1) player2 ++;

                     if (WasPairedThisRound.Count == players) { break; }

                     if (player1 == player2) { continue; }

​

                     if (WasPairedThisRound.Contains(player1)) { continue; }

                     if (WasPairedThisRound.Contains(player2)) { continue; }

                     if (ContainsPair(player1, player2)) { continue; }

​

                     Pair p = new Pair(player1, player2);

                     pairs.Add(p);

                     WasPairedThisRound.Add(player1);

                     WasPairedThisRound.Add(player2);

                     Game++;

                     TotalPairs++;

                     //listBox1.Items.Add($"{TotalPairs}. Round {round + 1}, game {Game}: [player {player1}] vs [player {player2}]");

​

                    Console.WriteLine($"{TotalPairs}. Round {round + 1}, game {Game}: [player {player1}] vs [player {player2}]");

                 }

​

                 // Exit the loop when pairs for the round are generated

                 if (WasPairedThisRound.Count == players) { break; }

​

             }

​

             Game = 0;

             //listBox2.Items.Add(WasPairedThisRound.Count.ToString()); ; // how much were paired each round? (debug)

             Console.WriteLine(WasPairedThisRound.Count.ToString()); ; // how much were paired each round? (debug)

             WasPairedThisRound.Clear(); // clear the list for the next loop of pairing

​

         }

​

​

         Console.WriteLine();

         Console.WriteLine("Show each player matchup");

         foreach(var player in Enumerable.Range(1,players))

         {

             Console.WriteLine($"Player: {player.ToString().PadLeft(2)}:  {(String.Join(", ", pairs.Where(x => x.Player1 == player || x.Player2 == player).Select(x => (x.Player1 == player ? x.Player2 : x.Player1).ToString().PadLeft(2))))}");

         }

​

​

​

     }

}

​

public class Pair

{

    public int Player1 { get; set; } = -1;

    public int Player2 { get; set; } = -1;

​

    public Pair(int p1, int p2)

    {

        Player1 = p1;

        Player2 = p2;

    }

}