The code for option 3 is quite confusing. It took me a while to figure out exactly what it was doing.

my @available = grep {
    $door[ $choice ] eq 'car' ? ( $_ != $choice ) : ( $doors[ $_ ] eq 
+'car' )
} 0 .. 2;
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Hmm.. I guess that's not much clearer either.

Update: so I rewrote the code, and I think this is clearer:

for ( 1 .. 100_000 ) {
    my @door = 0 .. 2;

    my $car_door = int rand @door;
    my $my_pick = int rand @door;

    @door = grep { $_ != $my_pick } @door;

    ## Option 1: The host reveals a goat
    #my @available = grep { $_ != $car_door } @door;

    # Option 2: The host opens a random unopened door
    #my @available = @door;

    ## Option 3: The host tries to be malicious
    #my @available = @door;
    #@available = grep { $_ == $car_door } @door if $my_pick != $car_d
+oor;

    my $opened = $available[ rand @available ];

    if( $opened == $car_door ) {
        $my_pick == $car_door ? $skip_car++ : $skip_goat++;
        next;
    }

    ## Count my wins if I stick or switch
    $my_pick == $car_door ? $stick++ : $switch++;
}
[download]