The link you gave shows an example but doesn't phrase criteria, which is unfortunate for a puzzle.

Please see How do I post a question effectively?

Supposing the frequency of letters has to be an ascending sequence. ..

I'm not aware of a possibility to sum the count of matches in pure ² m// regexes so probably it's possible in tr// but those can't backtrack.

Probably if you code 1..n matches for a fixed n into your regex and combine n look-aheads you can built an and condition. *

This wouldn't work for arbitrary big n though.

Cheers Rolf
(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!

*) that is find one letter exactly once and find one letter exactly twice and so on.

already the first term is too tricky for me...

²) no Perl embedded

update

First step: What is a regex to find one letter exactly once?

update

Waiting for tybalt89 ... tick tock tick tock ... ;)

In reply to Re: Puzzle Regex: Letter Frequency Arithmetic Sequence by LanX
in thread Puzzle Regex: Letter Frequency Arithmetic Sequence by QM

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.