Round Robin Tournament

This little ruby gem implements the Round Robin Tournament scheduling. It is useful when you want a competition "in which each contestant meets all other contestants in turn", or if you have a classroom of students and want them to work in pairs, but with a different partner every day.

Upgrade

If you upgrade from version 0.0.1 to 0.1.2, the tournament rotation has been reversed, which brings stability on first day pairs for a growing number for participants.

Installation

Add this line to your application's Gemfile:

gem 'round_robin_tournament'

And then execute:

$ bundle

Usage

Call the method RoundRobinTournament.schedule with one argument, an Array of size n. It will return an array of n - 1 elements, the days, and each element is an array of two elements, the game competitors.

If n is off, then the first element of each array element will be an array of two element, the last one being nil.

Example (n is even)

require "round_robin_tournament"

# Compute all the possible teams for each day in the classroom
students = %w(John Paul Ringo George)
teams = RoundRobinTournament.schedule(students)

# Print for each day, each team
teams.each_with_index do |day, index|
  day_teams = day.map { |team| "(#{team.first}, #{team.last})" }.join(", ")
  puts "Day #{index + 1}: #{day_teams}"
end

# Day 1: (Paul, George), (Ringo, John)
# Day 2: (Ringo, George), (John, Paul)
# Day 3: (John, George), (Paul, Ringo)

Example (n is odd)

require "round_robin_tournament"

# Compute all the possible teams for each day in the classroom
students = %w(John Paul Ringo George OtherGuy)
teams = RoundRobinTournament.schedule(students)

# Print for each day, each team
teams.each_with_index do |day, index|
  day_teams = day.map { |team| "(#{team.first}, #{team.last})" }.join(", ")
  puts "Day #{index + 1}: #{day_teams}"
end

# Day 1: (Paul, ), (Ringo, John), (George, OtherGuy)
# Day 2: (Ringo, ), (George, Paul), (OtherGuy, John)
# Day 3: (George, ), (OtherGuy, Ringo), (John, Paul)
# Day 4: (OtherGuy, ), (John, George), (Paul, Ringo)
# Day 5: (John, ), (Paul, OtherGuy), (Ringo, George)

Credits

I'd like to thank Pierre-Olivier Goffard, Joel Cohen and Florent Rovetta from the Institut de Mathématiques de Marseille who helped a lot!