How to find Prime Factors using Perl

What are Prime Factors? | Maths Explanation for Perl Kids

Finding prime factors is all about selecting those factors of a number that are prime.
The prime factors of 36 as an example, are:

2 X 2 X 3 X 3.

In this guide, we'll thoroughly explain prime factorisation and show how to code a Perl algorithm to find prime-factors in a detailed and interactive manner.
This Math exercise and Perl algorithm will help young students understand prime factorization by listing all prime factors of a number.

Step-by-step Guide to Prime Factorisation of Numbers in Perl

We'll go about the Perl algorithm to find prime factors in a simple way:

Step 1:

Starting with 2, find the first factor of the number of interest - this factor will definitely be a prime.
Store this factor away.

Step 2:

Divide number in question by found factor.

Step 3:

Using result from Step 2 as the new number in question (number whose prime factors we are trying to find), repeat Step 1.

Step 4:

Continue recursively until we arrive at 1.

Step 5:

Create a new Perl module file; File, New File.
Call it listPrimeFactors.pm.

Type out the adjoining Perl code for listing prime factors.

Perl Code for List Prime Factors - Module File.

package LISTPRIMEFACTORS;

BEGIN {
    require Exporter;

    # for the sake of standard
    our $VERSION = 2016.12;

    # Inherit from exporter to export functions and variables
    our @ISA = qw(Exporter);

    # Functions and variables to be exported by default
    our @EXPORT_OK = qw(onlyPrimeFactors);
}

use warnings;
use strict;
use POSIX qw(ceil);

my ($find_my_factors, $i);
my @found_prime_factors;

# simulate an object construct
# takes one argument  -- besides its name;
# value whose prime factors is to be found
sub new {
    no warnings;
    my $this = shift;
    my $parameters = {@_};
    bless $parameters, $this;
    $this->_init(@_);
    return $this;
}

# simulate a constructor
sub _init {
    my $self = shift;

    $find_my_factors = shift;
    @found_prime_factors = ();
    # STEP 1:
    $i = 2;
}

# takes one argument, the candidate for factorisation;
# returns an array reference of the prime factors
sub onlyPrimeFactors {
    my $in_question = $find_my_factors;
    $in_question = shift unless $_[0] eq __PACKAGE__;
    my $temp_limit;
    $temp_limit = ceil(sqrt($in_question));

    while ($i <= $temp_limit) {
        # STEP 4:
        # avoid an infinite loop with the i != 1 check.
        if ($i != 1 && ($in_question % $i) == 0) {
            push @found_prime_factors, $i;
            # STEPS 2, 3:
            return onlyPrimeFactors($in_question / $i);
        }
        $i++;
    }
    push @found_prime_factors, $in_question;

    return \@found_prime_factors;;
}

1;

Perl Code for List Prime Factors - Main Class.

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

# Useful variables
my ($test_guy, $answer);

# Use the list prime factors module/class
$test_guy = 97;
my $prime_factors = LISTPRIMEFACTORS->new($test_guy);
$answer = $prime_factors->onlyPrimeFactors();
print ("Prime factorising $test_guy gives:\n", join(" X ", @{$answer}), "\n");

print "\n\n";

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Perl Code to List Prime Pactors of a Number - Math Project for Primary Students