I don't suppose there's anything particularly creative about my attempts, and I'm sure they won't compare to the speed of C. But I've been looking for a reason to learn to use Benchmark, so I thought I'd give this a try.

I tried three methods: counting the characters with tr inside an eval, counting with s///g, and splitting the strings into arrays and using grep. Somewhat surprisingly (to me, anyway, as someone who very rarely uses eval), the eval/tr method was by far the slowest. I assume that's from the overhead of eval, but as far as I know, that's necessary, since the variable has to be interpolated. Perhaps it would be faster, as someone upthread suggested, to put the whole thing into a single eval, rather than 52 separate eval calls, but I'm too attached to keeping eval usage as minimal as possible to feel good about that. The grep method was better, but not great, even though I split the strings outside the test. The easy winner was using an s///g regex to count the replacements like tr, but without the need for eval. 

abaugher@bannor:~/work/perl/monks$ cat 938978.pl
#!/usr/bin/perl
use Modern::Perl;
use Benchmark qw(:all);;

my( $aa, $bb ) = ('','');

$aa .= chr(65 + rand(26)) for (1..50);
$bb .= chr(65 + rand(26)) for (1..50);
say $aa;
say $bb;

my @aa = split //, $aa;
my @bb = split //, $bb;

cmpthese(100000, {
    'grep' => \&usinggrep,
    'tr'   => \&usingtr,
    'sg'   => \&usingsg,
});

sub usinggrep {
    my $sum = 0;
    for my $l ('A'..'Z') {
        my $acount = grep /$l/, @aa;
        my $bcount = grep /$l/, @bb;
        $sum += abs($acount-$bcount);
    }
    return $sum;
}

sub usingtr {
    my $sum = 0;
    for my $l ('A'..'Z') {
        my $acount = eval "'$aa' =~ tr[$l][$l]";
        my $bcount = eval "'$bb' =~ tr[$l][$l]";
        $sum += abs($acount-$bcount);
    }
    return $sum;
}

sub usingsg {
    my $sum = 0;
    for my $l ('A'..'Z') {
        my $acount = $aa =~ s[$l][$l]g || 0;
        my $bcount = $bb =~ s[$l][$l]g || 0;
        $sum += abs($acount-$bcount);
    }
    return $sum;
}

abaugher@bannor:~/work/perl/monks$ perl 938978.pl
FHORAICOBMUCUMNYLRCUMVAMGXRRCADIZVTZTRENIEOBGNXSQT
JIPPTFERERTBOQOPNQSGWDTTOZOTHNXPEKJACSXEQBOAPIMSHI
       Rate   tr grep   sg
tr    924/s   -- -45% -88%
grep 1682/s  82%   -- -79%
sg   7849/s 749% 367%   --

[download]

Aaron B.
My Woefully Neglected Blog, where I occasionally mention Perl.

In reply to Re: The sum of absolute differences in the counts of chars in two strings. by aaron_baugher
in thread The sum of absolute differences in the counts of chars in two strings. by BrowserUk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.