monty_coin_problem.rb

# returns the two boxes ["G", "G"], ["G", "S"]  (equal odds for every order)
def get_boxes
  dice_roll = rand()
  if dice_roll < 0.25
    [["G", "G"], ["G", "S"]]
  elsif dice_roll < 0.5
    [["G", "G"], ["S", "G"]]
  elsif dice_roll < 0.75
    [["G", "S"], ["G", "G"]]
  else
    [["S", "G"], ["G", "G"]]
  end
end


# Always picks first coin from first box.
def place_bet
  boxes = get_boxes
  
  coin0 = boxes[0].pop
  
  if coin0 == "S"
    puts "No bet will be placed."
    "0"
  elsif coin0 == "G"
    coin1 = boxes[0].pop
    
    if coin1 == "S"
      puts "Bryce wins!"
      "B"   # Bryce won!
    elsif coin1 == "G"
      puts "William wins!"
      "W"
    end
  end
end

def percent_format_odds( f )
  sprintf( "%0.02f %", f * 100 )
end


def run_many_bets( n )
  results = Hash.new(0)
  
  n.times do
    result = place_bet
    results[result] += 1
  end

  w = results["W"]
  b = results["B"]
  z = results["0"]
  
  
  puts "William wins: #{w} (#{ percent_format_odds( w / n.to_f )})"
  puts "Bryce wins:   #{b} (#{ percent_format_odds( b / n.to_f )})"
  puts "Nobody wins:  #{z} (#{ percent_format_odds( z / n.to_f )})"
  
  puts "W/B ratio:  #{w / b.to_f} / 1"
  results
end



puts run_many_bets( 100000 ).inspect