(apologies in advance for this title - I couldn't think of a more explicit way to summarize the question.... ;-)

This code is used in a cryptogram solving script. After a pattern match for a word is pulled from a dictionary, I can usually find an exclusive single match, which happens often enough to make me happy, but many times there is a group of matches found that I've just ignored. But then it dawned on me that in some cases, especially those with just a few results, some of the letters DID match and I could use just those letters in my translation. I started working on a way of building a mask of just the matching letters.

The code below works, giving me a string mask (e.g. '-ou--e--' for 'yourself' and 'southern') and a hash containing the letters and positions that match, but I'm certain there must be a more efficient, faster, more elegant way to do this. I thought about a regex but that's a very weak area for me so I thought I'd throw this out there and see if I could learn something.

Any help towards my education is sincerely appreciated!

FYI and if it matters - I'm running on Windows XP with perl-5.10

#!/usr/bin/perl -w
use strict;

my %groups = ( 
    group1 => ['cooling', 'rooting', 'hooting', 'looking', 'doormat', 
+'cooking', 'cookies', 'noodles'], # desired result "-oo----"
    group2 => ['yourself', 'southern'], # desired result "-ou--e--"
    group3 => ['arden', 'arlen', 'asked'] # desired result "a--e-"
);

print " = = = = = = = = = = = = = = = = = = = \n\n";

foreach my $group (keys %groups) {
    my $mask = '';
    my %matches = ();
    my @group = @{$groups{$group}};
    foreach (@{$groups{$group}}) {
        print "\t$_\n";
    }

    my $group_count = $#group;
    my $group_length = length $group[0];
    print "group word count:$group_count group string length:$group_le
+ngth\n";
    for (my $i = 0; $i < $group_count +1; $i++) {
        for (my $j = 0; $j < $group_length; $j++) {
            if ($i) { 
                if (substr ($group[$i],$j,1) eq substr ($group[$i-1],$
+j,1)) { 
                    print substr ($group[$i],$j,1);
                    if (substr ($mask,$j,1) ne "-") {    substr ($mask
+,$j,1) = substr ($group[$i],$j,1); }
                    $matches{$j}++
                }
                else { 
                    print "-"; 
                    substr ($mask,$j,1) = "-";
                }
            }
        }
        if ($i) { 
            print "($group[$i-1])"; 
            print " ($group[$i])  ";
        }
        print " $mask\n";
    }
    print "\n";
    
    print "letter\t\tposition\n";
    foreach my $key (sort (keys(%matches))) {
        if ($matches{$key} == $group_count) {
            print  substr($group[0],$key,1), " \t\t$key \n";
        }
    }
    print "\n";
    print " = = = = = = = = = = = = = = = = = = = \n\n";
}
[download]

OUTPUT:
c:\mycode>perlmonk-code-example.pl
 = = = = = = = = = = = = = = = = = = =

        yourself
        southern
group word count:1 group string length:8

-ou--e--(yourself) (southern)   -ou--e--

letter          position
o               1
u               2
e               5

 = = = = = = = = = = = = = = = = = = =

        cooling
        rooting
        hooting
        looking
        doormat
        cooking
        cookies
        noodles
group word count:7 group string length:7

-oo-ing(cooling) (rooting)   -oo-ing
-ooting(rooting) (hooting)   -oo-ing
-oo-ing(hooting) (looking)   -oo-ing
-oo----(looking) (doormat)   -oo----
-oo----(doormat) (cooking)   -oo----
cooki--(cooking) (cookies)   -oo----
-oo--es(cookies) (noodles)   -oo----

letter          position
o               1
o               2

 = = = = = = = = = = = = = = = = = = =

        arden
        arlen
        asked
group word count:2 group string length:5

ar-en(arden) (arlen)   ar-en
a--e-(arlen) (asked)   a--e-

letter          position
a               0
e               3

 = = = = = = = = = = = = = = = = = = =
[download]