($word1 ^ $word2) =~ tr/\0//

##</code><code>##

my %bag;
my $total = 0;
foreach(split '', $word1) {
    $bag{$_}++;
}
foreach(split '', $word2) {
    if($bag{$_}) {
        $bag{$_}--;
        $total++;
    }
}
return $total;