Due to your manual $cnt it is surprisingly annoying to follow. Write a loop over the indices instead: for my $i ( 0 .. $#pre ).
I partly agree with you, which is why I voted your post ++ anyway. But isn't "surprisingly annoying" a bit excessive?!? As with lots of other things relating to readability and aesthetics in Perl (and not only!) I think that these are largely matters of personal taste. As far as I'm concerned I do not like to iterate over indices: not that i've never done it, but I tend to avoid it if possible...

However I would like to stress that the point I was focusing on was rather what to do than how to exactly do it, i.e. use some trick to let the "most probable" choice be the first one to be tested. Of course this only applies to situations (like the one I had under consideration in my personal experience) in which you know a priori that this strategy is likely to be more efficient.

As a side note if you want to see a yet more awkward (but IMHO still interesting) way to do it, please see the USENET article cited in the previous post!

And why splice+push (both linear operations) frequently if you can just do a bit of trivial index math?
Of course splice() and push() are expensive, but I use them only as needed, whereas you always do your "bit of trivial index math": all in all I do not expect my code to be less efficient than yours, nay, to be fair I expect it to be slightly more efficient. Of course we can verify this soon: 
#!/usr/bin/perl

use strict;
use warnings;
use Benchmark qw/:all :hireswallclock/;

my @ARGV0=@ARGV;
my @pre=map "../../pics/$_/", '00'..'16';

cmpthese 1000, { blazar => \&blazar,
                 aristotle =>\&aristotle }, 'all';

sub blazar {
    @ARGV=@ARGV0;
    while (<>) {
        chomp;
        my $cnt;
        for my $p (@pre) {
            local $_ = $p . $_;
            if (-e) {
                # print;
                push @pre, splice @pre, 0, $cnt if $cnt;
                last;
            }
            $cnt++;
        }
    } 
}

sub aristotle {
    @ARGV=@ARGV0;
    my $offs = 0;
    
    while ( <> ) {
        chomp;
        for my $i ( 0 .. $#pre ) {
            local $_ = $pre[ ( $i + $offs ) % @pre ] . $_;
            next if not -e;
            # print;
            $offs = $i;
            last;
        }
    }
}

__END__

[download]
I ran this on perl 5.8.6 under Linux (kernel 2.6.9) with a sample input file. This gives me: 
Benchmark: timing 1000 iterations of aristotle, blazar...
 aristotle: 20.2232 wallclock secs (14.14 usr  6.08 sys +  0.00 cusr  0.00 csys
= 20.22 CPU) @ 49.46/s (n=1000)
    blazar: 16.3845 wallclock secs ( 9.93 usr  6.45 sys +  0.00 cusr  0.00 csys
= 16.38 CPU) @ 61.05/s (n=1000)
            Rate aristotle    blazar
aristotle 49.5/s        --      -19%
blazar    61.1/s       23%        --
UPDATE: Honest of me to point out that I made a mistake preparing this benchmark. However please see a correct one at a later post of mine here below...

In reply to Re^2: Yet Another "Matching over a list of conditions"-like technique by blazar
in thread Yet Another "Matching over a list of conditions"-like technique by blazar

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