just playing around to solve this riddle: http://www.spiegel.de/wissenschaft/mensch/raetsel-der-woche-wie-viele-schliessfaecher-stehen-offen-a-1041982.html

Spiegel_riddle_2015_07_06.rb

#! /usr/bin/env ruby
# http://www.spiegel.de/wissenschaft/mensch/raetsel-der-woche-wie-viele-schliessfaecher-stehen-offen-a-1041982.html

require 'tco'

NUMBER_OF_DOORS = ARGV[0].to_i || 10
INITAL_STATE = false # false is closed, true is opened

DOORS = (1..NUMBER_OF_DOORS).map { false }

def run(n)
  DOORS.each_with_index do |door,index|
    if ((index+1) % n) == 0
      DOORS[index] = !DOORS[index]
    end
  end
end

def render
  DOORS.each do |d|
    if d
      print "  ".bg("#00DD00")
    else
      print "  ".bg("#DD0000")
    end
  end
  print "\n"
end

(1..NUMBER_OF_DOORS).each do |n|
  run(n)
  render()
end