Re: [FWP] Perl Card Games

[Chip Turner <chip@zfx.com>]

Brand Hilton <bhilton@adc.com> writes:

> On Tue, Aug 03, 1999 at 05:18:18PM -0400, Chip Turner wrote:
> > 
> > @cards = (0 .. 51); # or any number of them
> > $passes = 1; # one pass should be sufficient for all but the most paranoid
> > $cards[$_ % @cards] = $cards[rand(@cards) % @cards] foreach 0 .. ($passes * @cards - 1);
> 
> Untested, I presume :-)  Yours clobbers cards instead of swapping
> them.

That's what I get for not testing :)  You are of course correct that
it clobbers instead of shuffling.
 
> This is similar, but actually works:
> 
>   @cards = (0 .. 51); # or any number of them
>   $passes = 1; # one pass should be sufficient for all but the most paranoid
>   foreach (0 .. ($passes * @cards - 1)) {
>     $rand = rand(@cards);
>     @cards[$rand % @cards, $_ % @cards] = @cards[$_ % @cards, $rand % @cards];
>   }
> 
> Unfortunately, it lacks the nifty foreach-as-a-statement-modifier.

We can still use the infix foreach!  Never understimate the desire for
a Perl coder to use his or her favorite construct!

@cards = (0 .. 51); # or any number of them
$passes = 1; # one pass should be sufficient for all but the most paranoid

$i = rand(@cards) % @cards, @cards[$i, $_ % @cards] = @cards[$_ % @cards, $i] 
    foreach 0 .. ($passes * @cards - 1);

Hmm.  Still not perfect yet.

@cards = (0 .. 51); # or any number of them
$passes = 1; # one pass should be sufficient for all but the most paranoid

@a = (rand(@cards) % @cards, $_ % @cards), @cards[@a] = @cards[reverse @a]
    foreach 0 .. ($passes * @cards - 1);

That's maybe a bit better, but it's not pretty enough.  Hmm.  Too many
variables, not enough perl internals.  We can do better!

@cards = map { $_->[0] }
           sort { $a->[1] <=> $b->[1] }
             map { [ $_, rand(1 << 31) ] }
               (0 .. 51);

That has a certain aesthetic niceness to it.  I think someone did a
similar one earlier.  I'm not 100% convinced this is a truly random
sort, but I think it should be pretty good.  Hopefully the rand perl
uses (which I hope desperately isn't the default rand that the OS
comes with, but deep down I suspect it is) is decent enough to give a
good distribution.

> 'Course, if it was me, I'd just do
> 
>   use Algorithms::Numerical::Shuffle;
>   @cards = (0 .. 51); # or any number of them
>   @cards = shuffle(@cards)
> 
> Not as much fun, maybe, but a lot quicker to type and a lot less
> error-prone :-)

Aww not much fun at all! :)
Unless you count the intrinsic fun in using CPAN, which is pretty
high.

Okay that's enough fuy for now :)

Chip

-- 
Chip Turner                   chip@ZFx.com
                              Programmer, ZFx, Inc.  www.zfx.com
                              PGP key available at wwwkeys.us.pgp.net

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