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

my( $stick, $switch, $skip_goat, $skip_car ) = (0, 0, 0, 0);

for ( 1 .. 100_000 ) {
    ## Randomly hide the prizes behind the doors.
    my @doors = shuffle 'car', 'goat', 'goat';

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

    ####
    ## Uncomment the option you want here to see different scenarios.
    ###

    ## Option 1: The host opens a door that I didn't pick
    ## and that isn't the car
    #my @available = grep{ $_ != $choice and $doors[ $_ ] ne 'car' } 0 .. 2;

    ## Option 2: The host opens a random door
    #my @available = grep{ $_ != $choice } 0 .. 2;

    ## Option 3: The host tries to be malicious
    #my @available = grep{ $_ != $choice and $doors[ $_ ] eq 'car' } 0 .. 2;
    #@available = grep{ $_ != $choice } 0..2 if not @available;

    ####
    ## End of options
    ####

    # Monty chooses which door to open from the choices
    # that he might make.
    my $opened = $available[rand(@available)];

    if ($doors[$opened] eq 'car') {
        $doors[ $choice ] eq 'car' ? $skip_car++ : $skip_goat++;
        next;
    }

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

printf "Odds of
    Not getting here if you were originally right: %.3f
    Not getting here if you were originally wrong: %.3f
    Win if you don't switch: %.3f
    Win if you do switch: %.3f\n",
    $skip_car / (( $stick + $switch + $skip_goat + $skip_car) / 100 ),
    $skip_goat / (( $stick + $switch + $skip_goat + $skip_car) / 100 ),
    $stick / (( $stick + $switch) / 100 ),
    $switch / (( $stick + $switch) / 100 )