Hi derrick! Welcome aboard!
See below for my reply. On Tue, 02 May 2017 22:58:58 +0800 "derrick cope" <derr...@thecopes.me> wrote: > I was writing a program to solve the #3 exercise on project Euler. For reference, it is https://projecteuler.net/problem=3 . >I needed > to find the prime factors of a given number. I have solved it already but a > couple of the ways I tried to solve the problem caused a problem. > > The below worked for smaller numbers but when I used the 12 digit number > given by project Euler I got "Out of memory!" > > chomp( my $factor = <>); > my @primefactor = grep { &isprime( $_ ) } ( grep { $factor % $_ == 0 } > 1..$factor ); First of all, please go over http://perl-begin.org/tutorials/bad-elements/ and avoid these bad elements. add 'use strict;' and 'use warnings;' and avoid calling subroutines with ampersands. In that line's case you're building several very long lists. In this case a foreach loop will be better. Also not that you can also write the nested greps as grep { $factor % $_ == 0 and isprime($_)} ... . >sub isprime { > my $numb = shift; > my @quot = grep { > if ( $numb % $_ == 0 ) {1; > } else { 0;} > } 2..$numb-1; > unless ( @quot ) { > 1; > # say "prime"; > } else { > 0; > # say "not prime"; > } > } > your indentation is lacking, and better see http://perl-begin.org/tutorials/bad-elements/#grep_instead_of_any . Also use an explicit return and don't use if or unless to return a value. (you can try using the ? : ternary conditional operator instead). > > This one worked but caused my computer to crash. > my $xxx = 1; > while ( $xxx < $factor ) { > if ( $factor % $xxx == 0 and &isprime($xxx) ) { > say $xxx; > } > $xxx++ > } > what is causing perl to do this? Would using a module save memory?Thanks for > any help. That looks better memory wise. But "isprime()" is still sub-optimal. Note that you can optimise the algorithm considerably by using some tricks. See: https://duckduckgo.com/?q=project+euler+3&ia=web Perhaps see https://duckduckgo.com/?q=prime+factorization&ia=web too. Regards, Shlomi Fish -- ----------------------------------------------------------------- Shlomi Fish http://www.shlomifish.org/ https://youtu.be/n6KAGqjdmsk - “Hurt Me Tomorrow” I love being convinced that I was wrong before. That way I knew I improved and am now wiser. Like the Klingon warriors say when it happens: “What a great day it was for me to die!”. Please reply to list if it's a mailing list post - http://shlom.in/reply . -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
