Project Euler 23

PE23.pl

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;
use List::Util qw/sum/;

sub factor{
    my $n = shift;
    my %hash = ();

    for(my $i=2; $i*$i<=$n; $i++){
	while( $n % $i == 0 ){
	    $hash{$i}++;
	    $n /= $i;
	}
    }
    $hash{$n}++ if $n > 1;

    return %hash;
}

sub sum_of_divisor{
    my %hash = ($#_ == 0 ? %{$_[0]} : @_);
    my $res = 1;
    my $tmp = 1;

    return 0 if scalar(keys %hash) == 0;

    while( my ($a, $b) = each %hash ){
	$res *= ($a ** ($b + 1) - 1) / ($a - 1);
	$tmp *= $a ** $b;
    }
    return $res - $tmp;
}

my $m = 28123;
my @abundantNum = grep{sum_of_divisor(factor($_)) > $_} 1..$m;
my %S = ();

foreach my $i (0..$#abundantNum){
    foreach my $j ($i..$#abundantNum){
	last if $abundantNum[$i] + $abundantNum[$j] > $m;
	$S{ $abundantNum[$i] + $abundantNum[$j] } = 1;
    }
}

print sum grep{!exists($S{$_})} 1..$m;