I’m developing a function that determines if a list of items fits inside a box using the bin packing algorithm, which places the larger items first and then checks if the others fit in the remaining space (above and to the side).

The function below works, but sometimes it duplicates some data and I can’t figure out why.

I’ve tested with a lot of products, and sometimes it works fine, but sometimes it doesn’t and I can’t figure out why. I want to improve my code so it can return the right answer to any list of items.

Here’s my current code:

function fillBox(&$items, &$box, &$savedItems)
{

    foreach ($items as $key => $item) {
        $bin = $box;
        if ($item['width'] <= $box['width'] && $item['long'] <= $box['long'] && $item['height'] <= $box['height']) {
            // Change available box space
            $box['long'] -= $item['long'];
            // Modify bin
            $bin['long'] = $item['long'];
            $bin['width'] -= $item['width'];
            // Store items
            $savedItems[] = $item;
            // Remove item from array
            unset($items[$key]);
            // Start iterating through the bin
            fillBox($items, $bin, $savedItems);
        }
    }

    $result = empty($items) ? null : $items;

    $result = [$savedItems, $result];
    return $result;
}