sub encode {
    (my $string = shift) =~s/((.)\2*)/$2 . (length $1) /eg;
    $string;
}

##</code><code>##

sub group {
  my $x = shift;
  my $pos = 0;
  my @groups;
  $x =~ s{ ((.)\2*)
           (?{ push(@groups, [ substr($^N,0,1), $pos, $pos+length($^N) ]);
             $pos+=length($^N) })
         }{}gx;
  \@groups;
}