$am = $1 if $_[0] =~ /$mask/;
    $bm = $1 if $_[1] =~ /$mask/;

##</code><code>##

    ($am, $bm) = map {/$mask/ ? $1 : 0} @_;

##</code><code>##

@result = map {substr $_, 2}
          sort
          map {sprint "%02d%s", (/$mask/ ? $1 : 0), $_} @f;