Re^2: Unable to Understand grep and hash use for prime no.

The OP does not use grep and hashes to calculate prime numbers. It uses a subroutine called is_prime(), which is not included in the posted code.

Could you post your version, so we can learn from it?

The way forward always starts with a minimal test.

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Re^3: Unable to Understand grep and hash use for prime no. by danaj (Friar) on Aug 05, 2015 at 08:02 UTC
It looks like it is from "Beginning Perl" by Curtis Poe. Page 300 has the whole program, page 301 discusses is_prime() which is non-optimized trial division (checks divisibility by all integers up to sqrt(n)). Page 302 discusses the code in question which is introducing using a hash to cache the result. In particular, the test suite includes duplicates in its list. That's why the hash is used.	[reply]