First, I implemented the following simple version:

sub score
{
    my ($word1, $word2) = @_;

    # return a special value (defined somewhere in the file
    # if we have an exact match)
    return $words_equal if ($word1 eq $word2);

    my @chars1 = split(//, $word1);
    my @chars2 = split(//, $word2);
    my $count = 0;

    foreach $a (@chars1)
    {
        foreach $b (@chars2)
        {
            if ($a eq $b)
            {
                $count++;
                last;
            }
        }
    }

    return $count;
}
[download]

Then, I tried optimizing it. The following is a regexp version:

sub score2
{
    my ($word1, $word2) = @_;

    return $words_equal if ($word1 eq $word2);

    my @chars1 = split(//, $word1);
    my $count = 0;

    foreach $a (@chars1)
    {
        if ($word2 =~ /$a/)
        {
            $count++;
            last;
        }
    }

    return $count;
}
[download]

Benchmarking proved that the second version is about 50% slower than the first & simple one.

Any ideas on how this can be made faster ?

TIA, Spurperl