Beskin 31 problem - https://www.acmicpc.net/problem/14429

beskin.rb

class Game
  def initialize
    @rounds = []
  end

  def set(round)
    @rounds << round
  end

  def fastest_round
    fastest_round_length = @rounds.map { |round| round.length }.min
    @rounds.find { |round| round.length == fastest_round_length }
  end

  def fastest_round_info
    {
      order: @rounds.index(fastest_round) + 1,
      length: fastest_round.length
    }
  end
end

class Round
  attr_reader :max, :duration

  def initialize(max, duration)
    @max = max
    @duration = duration
    @all_numbers = [*1..@max]
  end

  def min_winning_num
    @all_numbers[(max-1) % (1+duration) - 1]
  end

  def winning_numbers
    @all_numbers.select do |number|
      (number - min_winning_num) % (1 + duration) == 0
    end
  end

  def length
    winning_numbers.length * 2
  end
end

@game = Game.new

total_rounds = gets.chomp.to_i
total_rounds.times do
  round_info = gets.chomp.split(' ')
  @game.set(Round.new(round_info[0].to_i, round_info[1].to_i))
end

puts "#{@game.fastest_round_info[:order]} #{@game.fastest_round_info[:length]}"

beskin_test.rb

require 'minitest/autorun'
require_relative 'beskin'

class TestGame < Minitest::Test
  def setup
    @game = Game.new

    @r1 = Round.new(31, 3)
    @r2 = Round.new(20, 6)
    @r3 = Round.new(14, 2)

    @game.set(@r1)
    @game.set(@r2)
    @game.set(@r3)
  end

  def test_can_create_each_round
    @round = Round.new(31, 3)
    assert_equal 31, @round.max
    assert_equal 3, @round.duration
  end

  def test_find_minimum_wining_number_of_round
    @round = Round.new(31, 3)
    assert_equal 2, @round.min_winning_num
  end

  def test_find_winning_numbers_of_round
    @round = Round.new(31, 3)
    assert_equal [2, 6, 10, 14, 18, 22, 26, 30], @round.winning_numbers
  end

  def test_return_length_of_round
    @round = Round.new(31, 3)
    assert_equal 16, @round.length
  end

  def test_game_takes_round
    assert_equal 3, @game.rounds.length
  end

  def test_find_fastest_round_of_game
    assert_equal @r2, @game.fastest_round
  end

  def test_return_info_of_the_fastest_round_of_the_game
    assert_equal 2, @game.fastest_round_info[:order]
    assert_equal 6, @game.fastest_round_info[:length]
  end

  def test_can_find_correct_info_with_many_rounds
    @game = Game.new

    @game.set(Round.new(79, 3))
    @game.set(Round.new(156, 7))
    @game.set(Round.new(24, 1))
    @game.set(Round.new(1053, 1052))
    @game.set(Round.new(3942, 12))
    @game.set(Round.new(152, 4))
    @game.set(Round.new(13, 5))
    @game.set(Round.new(2435, 241))
    @game.set(Round.new(32, 2))

    assert_equal 4, @game.fastest_round_info[:order]
    assert_equal 2, @game.fastest_round_info[:length]
  end
end