sub roy {
   my %count;
   while ($seq =~ /(?=(((.).).))/g) {
      ++$count{$1};
      ++$count{$2};
      ++$count{$3};
   }
   # pick up the last two chars
   $seq =~ /((.)(.))$/;
      ++$count{$1};
      ++$count{$2};
      ++$count{$3};
   1;
}