Famous Perl One-Liners Explained, Part III: Calculations

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41 pointsepi0Bauqu4 comments

The prime number detector is quite clever. It reminds me of the number based logic constructs from Godel's incompleteness theorem. It's essentially maps a mathematical concept to a string and operates on it.

For any unary integer greater than 1, the regular expression /^(11+?)\1+$/ matches it iff the number is not a prime. In other words, if there exists no integer less than the number itself and greater than one (first capturing group) that is a divisor of the number. The non-greedy + is also a nice touch, it will start out from the smallest factors and build from there.

that impressed me the most as well. the least lines I could do it in was 4.

the others I wasn't necessarily able to think of the one liner before checking the answer but I at least had a general idea of how it might be done. the primes completely stumped me.

Today I am low on creativity and can't think of more cool calculations. Can anyone help me out?

I just thought of one actually - sum up the size of files in a directory.

Can you think of more? ... Anything that comes to your mind.

Somebody asked me today how to write a script that would find all phrases (1 or more sequential words) in a text that appear more than once.

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