reducedProducts.php

<?php

/**
 * Returns an array with each position filled with the product of all
 * elements of the original array except for the one on the respective position
 *
 * @param array $arr
 *
 * @return array
 */
function reducedProducts(Array $arr)
{
    $l2r = [1];
    $r2l = [1];
    $arrSize = count($arr);

    for ($i = 0; $i < $arrSize - 1; $i++) {
        $l2r[] = $arr[$i] * $l2r[(count($l2r) - 1)];
        $r2l[] = $arr[$arrSize - 1 - $i] * $r2l[(count($r2l) - 1)];
    }

    $r2l = array_reverse($r2l);

    return array_map(function ($x, $y) {
        return $x * $y;
    },
        $l2r, $r2l);
}

/* Usage */

$arr = [1, 2, 3, 4];
var_dump(reducedProducts($arr));

//-> [24,12,8,6]