Monty Hall Monte Carlo

monty.rb

change_mind = true
attempts    = 1000
successes   = 0

attempts.times do
  prize_door  = rand(3)
  guess_door  = rand(3)
  other_doors = [0, 1, 2] - [prize_door, guess_door].uniq
  empty_door  = other_doors.sort_by { rand }.first
  alt_door    = ([0, 1, 2] - [guess_door, empty_door]).first

  final_guess = change_mind ? alt_door : guess_door
  successes += 1 if final_guess == prize_door
end

win_percent = successes.to_f / attempts.to_f * 100.0