Monty Hall problem/Empirical Proof

#!/usr/bin/perl

# Here's a Perl script with which to empirically test
# the Monty Hall problem.
# I'll admit that the results completely blew me away
# the first time I ran the program, and I still wonder
# if there isn't some odd bug which just happens to 
# make the numbers look the way they do...

# 9 Aug 2001
# -J

# Empirical test of the Monty Hall problem
# Run with -v to see each game.

$iterations = 10;  # How many games to play

@items = ("goat1", "goat2", "car");  #We'll number the items 0-2

$verbosity = 1 if $ARGV[0] eq "-v";

sub verbose {
    if($verbosity == 1) {
        print($_[0]);
    }
}

for(1..$iterations) {
    $door[0] = int rand 3;  # What's behind door #1?

    if($door[0] == 0) {
        $door[1] = 1 + (int rand 2); # Door #2 gets 1 or 2
        if($door[1] == 1) { $door[2] = 2; } else { $door[2] = 1; }
    }

    if($door[0] == 1) {
        $door[1] = 2 * (int rand 2); # Door #2 gets 0 or 2
        if($door[1] == 0) { $door[2] = 2; } else { $door[2] = 0; }
    }

    if($door[0] == 2) {
        $door[1] = int rand 2; # Door #2 gets 0 or 1
        if($door[1] == 0) { $door[2] = 1; } else { $door[2] = 0; }
    }

    verbose( "Door 1: $items[$door[0]]  Door 2: $items[$door[1]]  Door 3: $items[$door[2]]\n" );

    $contestant = int rand 3;
    verbose( "Contestant chooses door " . ($contestant+1) . ".\n" );

    # If the contestant picked the car, Monty picks either other door
    if($items[$door[$contestant]] eq "car") {
        $coinflip = int rand 2;
        if($contestant == 0) { $monty = ($coinflip ? 1 : 2); }
        if($contestant == 1) { $monty = ($coinflip ? 0 : 2); }
        if($contestant == 2) { $monty = ($coinflip ? 0 : 1); }
    }


    # Otherwise, he picks the other goat
    if($items[$door[$contestant]] eq "goat1") {
        if($contestant == 0) { $monty = ($items[$door[1]] eq "goat2" ? 1:2); }
        if($contestant == 1) { $monty = ($items[$door[0]] eq "goat2" ? 0:2); }
        if($contestant == 2) { $monty = ($items[$door[0]] eq "goat2" ? 0:1); }
    }

    if($items[$door[$contestant]] eq "goat2") {
        if($contestant == 0) { $monty = ($items[$door[1]] eq "goat1" ? 1:2); }
        if($contestant == 1) { $monty = ($items[$door[0]] eq "goat1" ? 0:2); }
        if($contestant == 2) { $monty = ($items[$door[0]] eq "goat1" ? 0:1); }
    }


    verbose( "Monty opens door " . ($monty+1) . ".\n" );


    $sticker = ($items[$door[$contestant]] eq "car") ? "wins" : "loses";
    $switcher = ($items[$door[$contestant]] eq "car") ? "loses" : "wins";

    verbose( "Sticker $sticker.  Switcher $switcher.\n\n" );
    if($sticker eq "wins") { $stickers++ }
    if($switcher eq "wins") { $switchers++ }
}

print "\nGrand totals:\nStickers: $stickers\nSwitchers: $switchers\n";