Generate a schedule for a round robin tournament in C#

[round robin tournament]

Click here to see a description of the algorithm the program uses to schedule a round robin tournament.

Function GenerateRoundRobinOdd returns an array where results[i, j] gives the opponent of team i in round j of the round robin tournament. This function works only for an odd number of teams. The link above explains the method.

private const int BYE = -1;

// Return an array where results(i, j) gives
// the opponent of team i in round j.
// Note: num_teams must be odd.
private int [,] GenerateRoundRobinOdd(int num_teams)
{
    int n2 = (int)((num_teams - 1) / 2);
    int[,] results = new int[num_teams, num_teams];

    // Initialize the list of teams.
    int[] teams = new int[num_teams];
    for (int i = 0; i < num_teams; i++) teams[i] = i;

    // Start the rounds.
    for (int round = 0; round < num_teams; round++)
    {
        for (int i = 0; i < n2; i++)
        {
            int team1 = teams[n2 - i];
            int team2 = teams[n2 + i + 1];
            results[team1, round] = team2;
            results[team2, round] = team1;
        }

        // Set the team with the bye.
        results[teams[0], round] = BYE;

        // Rotate the array.
        RotateArray(teams);
    }

    return results;
}

Helper function RotateArray rotates the items in the team array. The algorithm calls this routine after each round.

// Rotate the entries one position.
private void RotateArray(int[] teams)
{
    int tmp = teams[teams.Length - 1];
    Array.Copy(teams, 0, teams, 1, teams.Length - 1);
    teams[0] = tmp;
}

Function GenerateRoundRobinEven returns a similar array for an even number of teams. It calls GenerateRoundRobinOdd to make a schedule for a tournament with one fewer teams. It then expands the result array and replaces the byes with the additional team. See the link above for a more complete explanation.

private int[,] GenerateRoundRobinEven(int num_teams)
{
    // Generate the result for one fewer teams.
    int[,] results = GenerateRoundRobinOdd(num_teams - 1);

    // Copy the results into a bigger array,
    // replacing the byes with the extra team.
    int[,] results2 = new int[num_teams, num_teams - 1];
    for (int team = 0; team < num_teams - 1; team++)
    {
        for (int round = 0; round < num_teams - 1; round++)
        {
            if (results[team, round] == BYE)
            {
                // Change the bye to the new team.
                results2[team, round] = num_teams - 1;
                results2[num_teams - 1, round] = team;
            }
            else
            {
                results2[team, round] = results[team, round];
            }
        }
    }

    return results2;
}

Function GenerateRoundRobin simply calls functions GenerateRoundRobinOdd and GenerateRoundRobinEven depending on whether the number of teams is odd or even.

private int[,] GenerateRoundRobin(int num_teams)
{
    if (num_teams % 2 == 0)
        return GenerateRoundRobinEven(num_teams);
    else
        return GenerateRoundRobinOdd(num_teams);
}


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4 Responses to Generate a schedule for a round robin tournament in C#

  1. Andy Boot says:

    Fantastic piece of code, this saved me a great amount of time on a golf fixture generator for my clients website. Thanks alot. This has been bookmarked.

  2. Pingback: Algoritmos: Round Robin | ñoño Blog

  3. Sandeep Rawat says:

    Do you have such Algo for Single elimination and Double elimination too?

    • RodStephens says:

      Those are generally easier because you can use a pre-built bracket. If you google for “single elimination brackets” or “double elimination brackets” you should see a lot of choices for tournaments with different numbers of teams.

      If you have an odd number of teams, give some of the top teams byes. For example, if you have 7 teams, use an 8 team bracket and give the top seeded team a bye in round 1.

      Let me know if you have special needs that won’t fit these sorts of brackets.

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