segmentation fault in perl grep function

Question

working on Euler problem 3

The prime factors of 13195 are 5, 7, 13 and 29.
What is the largest prime factor of the number 600851475143 ?

here is my Perl code just try to get all the factors first but it got segmentation fault, my Perl age is just about 2 month, could not figure out why. Segmentation fault 11 when I run it.

 #!/usr/bin/perl
 use warnings; 
 use strict;

 my $number = 600851475143;
 my @factors = grep {$number % $_ == 0} (1..$number);
 print @factors;

Run it again with sudo, no more segmentation fault but nothing printed out.

(1..$number) will generate an 2T array. Are you using a 64-bit OS? — Lee Duhem
– Lee Duhem, Commented Feb 28, 2014 at 3:07
Yes, Mac OS X 10.8.5, perlbrew Perl 5.18.2. Tried bigint as well, did not make any difference. — Ask and Learn
– Ask and Learn, Commented Feb 28, 2014 at 3:10
I guess it is still because you are trying to allocate too many memories. — Lee Duhem
– Lee Duhem, Commented Feb 28, 2014 at 3:25
agreed, even after I removed last 3 digits (so 1000 times smaller). It printed out "Out of Memory!" on my Linux VM, used all my remaining 12G RAM on my MacBook Pro. Will try something else — Ask and Learn
– Ask and Learn, Commented Feb 28, 2014 at 3:45

Miller · Accepted Answer · 2014-02-28 04:08:24Z

3

Code from googling "euler problem 3" and translating the python code.

use strict;
use warnings;

sub largest_prime_factor {
    my $n = shift;

    my $largest_factor = 1;

    # remove any factors of 2 first
    while ($n % 2 == 0) {
        $largest_factor = 2;
        $n /= 2;
    }

    # now look at odd factors
    my $p = 3;
    while ($n != 1) {
        while ($n % $p == 0) {
            $largest_factor = $p;
            $n /= $p;
        }
        $p += 2
    }

    return $largest_factor
}

print largest_prime_factor(600851475143);

1;

__END__

Or relying on good ole cpan:

use Math::Prime::Util qw(factor);
use List::Util qw(max);

use strict;
use warnings;

print max factor(600851475143);

edited Feb 28, 2014 at 4:08

answered Feb 28, 2014 at 3:57

Miller

35.3k4 gold badges42 silver badges61 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

DanaJ Over a year ago

CPAN solution slightly easier now: perl -E 'use ntheory ":all"; say vecmax(factor(600851475143));'

Collectives™ on Stack Overflow

segmentation fault in perl grep function

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related