Edit: I thought I had a better version but no. I ran the same benchmark again and the results were not the same at all (actually the three solutions had very similar performances). Something went wrong with my first attempt

You can get even better results if you remove the use of captures and backreferences: 

sub v6 {
    %subs = ();
    $subs{$&}++ while $string =~ m{A{2,}|C{2,}|G{2,}|T{2,}}g;
    } # v6

[download]
      Rate   v4   v5   v6
v4 55470/s   --  -9% -39%
v5 60734/s   9%   -- -34%
v6 91365/s  65%  50%   --

[download]

Edit: now that's a bad choice of delimiter 😂

I'm actually consistantly getting result that are worse without backreferences which which I don't understand...

In reply to Re^2: substrings that consist of repeating characters by Eily
in thread substrings that consist of repeating characters by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.