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

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Re^2: Unable to Understand grep and hash use for prime no. by Anonymous Monk on Aug 04, 2015 at 12:01 UTC
... used or instead of an if-statement because, when using grep, he had to. No, s/he didn't "have" to. `print "$_\n" for grep { if ($_%2) {$a=1} else {$a=0} $a } 1..10;` [download] Yes, it's uglier, but possible.	[reply] [d/l]
Re^2: Unable to Understand grep and hash use for prime no. by 1nickt (Canon) on Aug 04, 2015 at 15:21 UTC
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.	[reply] [d/l]
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]