Re: Prime Number Finder

[eisenstein]

I offer the following as a balance of speed, elegance, and brevity, or at the very least, a demonstration of TMTOWTDI. The algorithm is: take the first number off the top of the list, call it a prime, filter the rest of the list for multiples, repeat.

use strict;

sub primes {
    my @n = (2..shift);
    my @p;
    while (@n && (push @p, shift @n)) {
        @n = grep { $_ % $p[-1] } @n;
    }
    return @p
}

# find all primes through 100
print join ',',primes(100);

Note: the grep is fairly costly. Find a better algorithm if you're looking for all primes up to, say, 100,000.