Project Euler Problem 1 PHP Version

Project Euler Problem 1.php

<?php
#単純に加算
$sum = 0;
foreach (range(1, 999) as $i)
{
    if      (($i % 3) == 0) $sum += $i;
    elseif  (($i % 5) == 0) $sum += $i;
}
echo "$sum", "\n";
 
#等差数列の和
$sum = 0;
#初項, 公差
foreach( array(3, 5, 15) as $a )
{
    $n = (int)(999 / $a); #項数
    $l = $n * $a;         #末項 a＋(n－1)d
 
    switch ($a)
    {
        case 3:
        case 5:
            $sum += (($a + $l) * $n / 2);
            break;
        default:
            $sum -= (($a + $l) * $n / 2);
            break;
    }
}
echo "$sum", "\n";
?>