How on Earth does ^.?$|^(..+?)\1+$ produce primes?

Comments · 2.3K

• ST

  @standupmaths · 1 year ago · pinned

  Take your personal data back with Incogni! Use code standupmaths at the link below and get 60% off an annual plan: <a href="https://incogni.com/standupmaths">https://incogni.com/standupmaths</a><br><br>Don’t use code ^.?$|^(..+?)\1+$.

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• GR

  @Graphene_314 · 1 year ago

  The plural of regex is regrets.

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• YO

  @Yogarine · 1 year ago (edited)

  Regular expressions are already scary by nature. Making one that produces primes is truly terrifying.

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• CM

  @Cmanorange · 1 year ago

  wow, what a neat trick! i&apos;m adding this to my production code immediately, good luck new hires!

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• SC

  @scottieapplseed · 1 year ago

  I loved the home joke at the end; you&apos;re such a good localhost.

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• RM

  @RMDragon3 · 1 year ago (edited)

  To simplify, this takes the number and expresses it as a unary numeral system, where the number of marks is the value of the number you put in (e.g. 1 is 1, 2 is 11, 3 is 111, ...). The regex then looks to divide the unary representation into exactly N groups of size M, where both N and M are natural numbers with value 2 or larger. For example, you can divide 4 (represented as 1111) into 2 groups of &quot;11&quot;. You can divide 6 (represented 111111) into 2 groups of &quot;111&quot; or 3 groups of &quot;11&quot;. However, you can&apos;t divide 3 (represented as 111) into groups of the same size (technically you can do 3 groups of &quot;1&quot;, but then M isn&apos;t 2 or larger). &nbsp;Basically, you are checking if the number has any factors bigger than 1, which obviously is only false for prime numbers.

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• TE

  @tempest_dawn · 1 year ago

  love that the halloween horror episode on a math channel is . . . code

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• BU

  @busyfreeguy · 1 year ago

  15+ years of programming experience including using regular expressions and I still watched and enjoyed this video. It&apos;s a testament to Matt&apos;s enthusiasm and his skill as a speaker/teacher.

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• MC

  @mckseal · 1 year ago

  Regex is already halloween worthy.

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• TO

  @tostadojen · 1 year ago

  <b>Matt:</b> &quot;What the factor?&quot;<br><b>Primes:</b> &quot;Your factors can&apos;t help you here.&quot;

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• LI

  @linguica · 1 year ago

  I love regular expressions. I taught myself to use them in college and then as an intern doing data entry I was able to complete a full day&apos;s &quot;work&quot; in like 30 minutes.

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• RO

  @Rohanology27 · 1 year ago (edited)

  What in the ^.?$|^(..+?)\1+$ did I just watch?<br><br>Edit: Added

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