Cartesian product

cartesian-product.php

<?php

function multiply(...$sets): array
{
    if (!$sets) {
        return [[]];
    }
    $set = array_shift($sets);
    $products = multiply(...$sets);
    $result = [];
    foreach ($set as $value) {
        foreach ($products as $product) {
            array_unshift($product, $value);
            $result[] = $product;
        }
    }
    
    return $result;
}