Select Code to Download

use 5.18.0;
use warnings;
...

$subs{$_}++ for grep { length >= 2 } split m/,/ => ($string =~ s/([ACG
+T])\K(?!\1)/,/gr);
printf "%5d %3d %s\n", $subs{$_->[1]}, @$_ for sort { $b->[0] <=> $a->
+[0] || $a->[1] cmp $b->[1] } map {[ length, $_ ]} keys %subs;

    1   6 CCCCCC
    1   4 GGGG
...
    2   2 AA
    2   2 GG
    5   2 TT