But isn't "surprisingly annoying" a bit excessive?!?

It's what it is. It took me a moment of staring to figure out that you were doing something much simpler than the code suggested at first glance.

As far as I'm concerned I do not like to iterate over indices

Instead you iterate over elements and increment $cnt for each one. A rose by any other name… Neither do I like to, btw. I'm usually the one telling people not to. But when that's what's gotta be done, then that's what's gotta be done. (Perl6, as always, will have the solution, but alas, it's so far away yet…)

i.e. use some trick to let the "most probable" choice be the first one to be tested.

In that case I'd bubble single elements to the top. That retains memory of second-, third-, etc most likely matches based on previous data. Depending on the patterns in your data that may or may not be more, less or equally efficient.

while ( <> ) {
    chomp;
    for my $i ( 0 .. $#pre ) {
        local $_ = $pre[ $i ] . $_;
        next if not -e;
        print;
        @pre[ 0 .. $i ] = @pre[ $i, 0 .. $i - 1 ] if $i;
        last;
    }
}

[download]

I'm too lazy to set up a test environment to benchmark this, sorry. Depending on how much the array lookup costs it might pay to maintain the counter explicitly as you did in your code, though I can't quite believe that.

Note that in your case, a chdir '../../pics/' might speed things up quite a bit if you're testing a lot of files, since stat(2) won't have to traverse the same directories over and over for each and every single file test.

Makeshifts last the longest.

In reply to Re^3: Yet Another "Matching over a list of conditions"-like technique by Aristotle
in thread Yet Another "Matching over a list of conditions"-like technique by blazar

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