#! perl -slw
use strict;
use List::Util qw[ shuffle ];

our $TRIALS ||= 1_000_000;
my $DIVISOR = $TRIALS / 100;

my( $stick, $switch, $loseEitherWay );

for my $try ( 1 .. $TRIALS ) {
      ## Randomly hide the prizes behind the doors.
	my @doors = shuffle 'car', 'goat', 'goat';

      ## Pick a door
	my $choice = int rand 3;

      ## The host opens a door that I didn't pick
	my $opened = ( grep{ $_ != $choice } 0 .. 2 ) [ rand 2 ];

      ## If the host picks the car, I lose anyway.
	$loseEitherWay++, next if $doors[ $opened ] eq 'car';

      ## Count my  wins if I stick or switch
	$doors[ $choice ] eq 'car' ? $stick++ : $switch++;
}

printf "Odds of
	Losing either way: %.3f
	Win if you don't switch: %.3f
	Win if you do switch: %.3f\n", 
	$loseEitherWay / $DIVISOR, $stick / $DIVISOR, $switch / $DIVISOR;

__END__
P:\test>384288
Odds of
        Losing either way: 33.370
        Win if you don't switch: 33.307
        Win if you do switch: 33.324

P:\test>384288 -TRIALS=5000000
Odds of
        Losing either way: 33.318
        Win if you don't switch: 33.336
        Win if you do switch: 33.346