Project Euler Problem 1 Perl Version

Project Euler Problem 1.pl

use strict;
use warnings;
 
#単純に加算
my $sum = 0;
for (1..999)
{
    if      (($_ % 3) == 0) {   $sum += $_; }
    elsif   (($_ % 5) == 0) {   $sum += $_; }
}
print "$sum\n";
 
#等差数列の和
$sum = 0;
#初項, 公差
foreach my $a (3, 5, 15)
{
    my $n = int(999 / $a); #項数
    my $l = $n * $a;       #末項 a＋(n－1)d
 
    if      ($a == 3)   {   $sum += (($a + $l) * $n / 2);   }
    elsif   ($a == 5)   {   $sum += (($a + $l) * $n / 2);   }
    elsif   ($a == 15)  {   $sum -= (($a + $l) * $n / 2);   }
}
print "$sum\n";