Monty Hall Simulation done in readable ruby.

MontyHall.rb

#!/usr/bin/ruby

$door_count = 3
$door_list = 0.upto($door_count - 1).to_a
$game_count = 10 * 1000 

def percent(numerator, denominator)
  return "%5.2f%" %[100 * numerator.to_f / denominator.to_f]
end

puts "Door Count: #{$door_count}"
def coin_monty
  puts "Coin Flip simulation: There may be 0-#{$door_count} goats or prizes. We flip a 2 sided coin to determine it."

  switch_win = 0
  stay_win = 0

  $game_count.times { 

    prizeList = []

    # We toss a coin and then add a prize to the door
    # if the coin is heads (1)
    0.upto($door_count - 1) { | door |
      prizeList << door if rand(2) == 1
    }

    # You pick a random dooor.
    start = rand($door_count)
    
    doors = $door_list

    # Monty dismisses a losing door.
    if (doors - prizeList).length > 0
      dismiss = (doors - (prizeList + [start])).choice
    else
      # or a winning door if there are no losing doors.
      dismiss = (doors - [start]).choice
    end

    doors -= [start, dismiss]

    # The door you switch to will be the one that 
    # wasn't dismissed and that wasn't the one that
    # you started with.
    switch = doors.first
    
    # If you switched.
    switch_win += 1 unless prizeList.index(switch).nil?

    # puts "(%s) %s" %[prizeList.join(', '), start.to_s]
    # If you stayed.
    stay_win += 1 unless prizeList.index(start).nil?
  }

  puts "After #{$game_count} games:"
  puts "%28s %s" %[ "switching won the prize:", percent(switch_win, $game_count)]
  puts "%28s %s" %[ "staying won the prize:", percent(stay_win, $game_count)]
  puts ""
end
def rude_monty
  puts "Rude Monty simulation: Monty will never pick the prize but may pick your door, in which you move over your initial door choice."

  switch_win = 0
  stay_win = 0

  $game_count.times { 

    # Prize is behind a random door.
    prize = rand($door_count)

    # You pick a random dooor.
    start = rand($door_count)
    
    doors = $door_list

    # Monty dismisses a losing door.
    dismiss = (doors - [prize]).choice

    # If that was my door, I have to switch
    if dismiss == start
      start = (doors - [dismiss]).choice
    end

    doors -= [start, dismiss]

    # The door you switch to will be the one that 
    # wasn't dismissed and that wasn't the one that
    # you started with.
    switch = doors.first
    
    # If you switched.
    switch_win += 1 if switch == prize

    # If you stayed.
    stay_win += 1 if start == prize
  }

  puts "After #{$game_count} games:"
  puts "%28s %s" %[ "switching won the prize:", percent(switch_win, $game_count)]
  puts "%28s %s" %[ "staying won the prize:", percent(stay_win, $game_count)]
  puts ""
end
def smart_monty
  puts "Smart Monty simulation: Monty will never pick the prize."

  switch_win = 0
  stay_win = 0

  $game_count.times { 

    # Prize is behind a random door.
    prize = rand($door_count)

    # You pick a random dooor.
    start = rand($door_count)
    
    doors = $door_list

    # Monty dismisses a losing door.
    dismiss = (doors - [start, prize]).choice

    doors -= [start, dismiss]

    # The door you switch to will be the one that 
    # wasn't dismissed and that wasn't the one that
    # you started with.
    switch = doors.first
    
    # If you switched.
    switch_win += 1 if switch == prize

    # If you stayed.
    stay_win += 1 if start == prize
  }

  puts "After #{$game_count} games:"
  puts "%28s %s" %[ "switching won the prize:", percent(switch_win, $game_count)]
  puts "%28s %s" %[ "staying won the prize:", percent(stay_win, $game_count)]
  puts ""
end

def dumb_monty
  puts "Dumb Monty simulation: Monty may pick the prize."

  switch_win = 0
  stay_win = 0
  loss_count = 0
  played_on_count = 0

  $game_count.times { 

    # Prize is behind a random door.
    prize = rand($door_count)

    # You pick a random dooor.
    start = rand($door_count)
    
    # Monty dismisses a random door, which may have the prize.
    dismiss = ($door_list - [start]).choice

    # If it had the prize, then you lose.
    if (dismiss == prize)
      loss_count += 1
    else
      # Otherwise, we continue.
      played_on_count += 1

      # The door you switch to will be the one that 
      # wasn't dismissed and that wasn't the one that
      # you started with.
      switch = ($door_list - [start, dismiss]).first
      
      # If you switched.
      switch_win += 1 if switch == prize

      # If you stayed.
      stay_win += 1 if start == prize
    end
  }

  puts "After #{$game_count} games:"
  puts " You lost, because Monty picked the prize: #{percent(loss_count, $game_count)}"
  puts ""
  puts "%28s %s" %[ "switching won the prize:", percent(switch_win, played_on_count)]
  puts "%28s %s" %[ "including times lost:", percent(switch_win, $game_count)]
  puts ""
  puts "%28s %s" %[ "staying won the prize:", percent(stay_win, played_on_count)]
  puts "%28s %s" %[ "including times lost:", percent(stay_win, $game_count)]
  puts ""
end

smart_monty
rude_monty
dumb_monty
coin_monty

Door Count: 3
Smart Monty simulation: Monty will never pick the prize.
After 10000 games:
switching won the prize: 67.74%
staying won the prize: 32.26%

Rude Monty simulation: Monty will never pick the prize but may pick your door, in which you move over your initial door choice.
After 10000 games:
switching won the prize: 50.15%
staying won the prize: 49.85%

Dumb Monty simulation: Monty may pick the prize.
After 10000 games:
Monty picked the prize: 32.69%

switching won the prize: 50.20%
   including times lost: 33.79%

  staying won the prize: 49.80%
   including times lost: 33.52%

Coin Flip simulation: There may be 0-3 goats or prizes. We flip a 2 sided coin to determine it.
After 10000 games:
switching won the prize: 75.25%
staying won the prize: 49.94%