ch10.024_best

Perl Best Practices the source code

##############################################################################
##   Code fragment (Recommended) from Chapter 10 of "Perl Best Practices"   ##
##     Copyright (c) O'Reilly & Associates, 2005. All Rights Reserved.      ##
##  See: http://www.oreilly.com/pub/a/oreilly/ask_tim/2001/codepolicy.html  ##
##############################################################################


# Standard modules...
use strict;
use warnings;
use IO::Prompt;
use Carp;
use English qw( -no_match_vars );
use Data::Alias;
use Readonly;

use List::MoreUtils qw( uniq );

# This is a *really* bad factoring algorithm...
sub factors_of {
    my ($n) = @_;
    my @factors;
    for my $possible_factor (2..int sqrt($n)) {
        next if $n % $possible_factor;
        push @factors, $possible_factor;
        push @factors, $n / $possible_factor;
    }
    return sort {$a <=> $b} uniq @factors;
}


for my $n (2..1_000_000_000) {
    my @factors = factors_of($n);
 
    if (@factors == 2) {
        print "$n is prime\n";
    }
    else {
        print "$n is composite with factors: @factors\n";
    }
}