Ping pong league

league.rb

#!/usr/bin/env ruby

# Based on: http://en.wikipedia.org/wiki/Round-robin_tournament

def matches_schedule(players_count)
  schedule = {}

  matchdays = players_count - 1
  matches_per_day = middle = players_count / 2

  list = (1..players_count).to_a
  list_1 = list[0..middle-1]
  list_2 = list[middle..players_count-1]

  1.upto(matchdays) do |matchday|
    schedule[matchday] = matches_per_day.times.map do |i|
      [list_1[i], list_2[i]]
    end.shuffle

    list_2 << list_1.pop
    up, *list_2 = list_2
    list_1.insert(1, up)
  end

  schedule
end

# assume players is a list of strings, each containing the name of the player

players << '(descans)' unless players.count % 2 == 0

matches_schedule(players.count).each do |matchday, matches|
  puts "======================="
  puts "Match day #{matchday}"
  puts "======================="

  matches.each do |player_1, player_2|
    puts "#{players[player_1-1]} - #{players[player_2-1]}"
  end
end