my $string = "AAATTTAGTTCTTAAGGCTGACATCGGTTTACGTCAGCGTTACCCCCCAAGTTATTGGGGACTTT";
my %expect = qw( CCCCCC 1 GGGG 1 AAA 1 TTT 3 AA 2 GG 2 TT 5 );

use Test::More;
use Benchmark qw(cmpthese);

my %subs;

sub v1 {
    %subs = ();
    $subs{$_}++ for grep { length >= 2 } split m/,/ => ($string =~ s/([ACGT])\K(?!\1)/,/gr);
    } # v1

sub v2 {
    %subs = ();
    $subs{$_}++ for grep m/^([ACGT])\1+$/ => split m/,/ => ($string =~ s/(\w)\K(?!\1)/,/gr);
    } # v2

sub v3 {
    %subs = ();
    $subs{$_}++ for $string =~ m/(AA+|CC+|GG+|TT+)/g;
    } # v3

sub v4 {
    %subs = ();
    $subs{$1}++ while $string =~ m{(([ACGT])\2+)}g;
    } # v4

sub v5 {
    %subs = ();
    $subs{$&}++ while $string =~ m{([ACGT])\1+}g;
    } # v5

v1 (); is_deeply (\%subs, \%expect, "v1");
v2 (); is_deeply (\%subs, \%expect, "v2");
v3 (); is_deeply (\%subs, \%expect, "v3");
v4 (); is_deeply (\%subs, \%expect, "v4");
v5 (); is_deeply (\%subs, \%expect, "v5");

printf "%5d %3d %s\n", $subs{$_->[1]}, @$_ for sort { $b->[0] <=> $a->[0] || $a->[1] cmp $b->[1] } map {[ length, $_ ]} keys %subs;

cmpthese (-2, { v1 => \&v1, v2 => \&v2, v3 => \&v3, v4 => \&v4, v5 => \&v5 });

done_testing;