monty_hall.rb

require "benchmark"

ITERATIONS = (ARGV[0] || 10000).to_i

def pick(set)
  set[rand(set.size)]
end

def trial(method)
  wins = 0
  ITERATIONS.times do
    wins+=1 if send(method)
  end
  "#{method}: {iterations:#{ITERATIONS}, rate:#{wins*1.0/ITERATIONS}}"
end

def marek_ruby
  # randomize doors for good measure :)
  doors = [:one, :two, :three].shuffle
  
  winner = [pick(doors)]
  losers = doors - winner
  choice = pick(doors)

  if winner.include?(choice)
    # open random junk door
    doors -= [pick(losers)]
  else
    # open opposite junk door
    doors -= (losers - [choice])
  end

  # switch choice
  doors -= [choice]
  
  # return
  doors == winner
end

def marek_c
  door_win = rand(3)
  door_guess = rand(3)
  case door_guess
  when 0
    door_open = door_win == 1 ? 2 : 1
    switch_door = door_open == 2 ? 1 : 2
  when 1
    door_open = door_win == 0 ? 2 : 0
    switch_door = door_open == 2 ? 0 : 2
  when 2
    door_open = door_win == 0 ? 1 : 0
    switch_door = door_open == 1 ? 0 : 1
  end
  switch_door == door_win
end

buffer = []
Benchmark.bm(10) do |b|
  [:marek_ruby, :marek_c].each do |m|
    b.report m.to_s do
      buffer << trial(m)
    end
  end
end

puts buffer
#                 user     system      total        real
# marek_ruby  0.080000   0.000000   0.080000 (  0.074415)
# marek_c     0.000000   0.000000   0.000000 (  0.006399)
# marek_ruby: {iterations:10000, rate:0.6668}
# marek_c: {iterations:10000, rate:0.666}