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<?php |
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/** |
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* Box packing (3D bin packing, knapsack problem). |
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* |
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* @author Doug Wright |
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*/ |
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declare(strict_types=1); |
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namespace DVDoug\BoxPacker; |
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use function array_filter; |
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use function array_merge; |
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use function count; |
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use function iterator_to_array; |
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use Psr\Log\LoggerAwareInterface; |
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use Psr\Log\LoggerAwareTrait; |
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use Psr\Log\LogLevel; |
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use Psr\Log\NullLogger; |
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use function usort; |
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/** |
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* Actual packer. |
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* |
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* @author Doug Wright |
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* @internal |
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*/ |
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class WeightRedistributor implements LoggerAwareInterface |
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{ |
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use LoggerAwareTrait; |
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/** |
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* List of box sizes available to pack items into. |
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* |
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* @var BoxList |
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*/ |
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private $boxes; |
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/** |
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* Constructor. |
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*/ |
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public function __construct(BoxList $boxList) |
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{ |
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$this->boxes = $boxList; |
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$this->logger = new NullLogger(); |
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} |
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/** |
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* Given a solution set of packed boxes, repack them to achieve optimum weight distribution. |
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*/ |
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public function redistributeWeight(PackedBoxList $originalBoxes): PackedBoxList |
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{ |
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$targetWeight = $originalBoxes->getMeanWeight(); |
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$this->logger->log(LogLevel::DEBUG, "repacking for weight distribution, weight variance {$originalBoxes->getWeightVariance()}, target weight {$targetWeight}"); |
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/** @var PackedBox[] $boxes */ |
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$boxes = iterator_to_array($originalBoxes); |
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usort($boxes, function (PackedBox $boxA, PackedBox $boxB) { |
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return $boxB->getWeight() <=> $boxA->getWeight(); |
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}); |
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do { |
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$iterationSuccessful = false; |
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foreach ($boxes as $a => &$boxA) { |
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foreach ($boxes as $b => &$boxB) { |
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if ($b <= $a || $boxA->getWeight() === $boxB->getWeight()) { |
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continue; //no need to evaluate |
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} |
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$iterationSuccessful = $this->equaliseWeight($boxA, $boxB, $targetWeight); |
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if ($iterationSuccessful) { |
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$boxes = array_filter($boxes, function (?PackedBox $box) { //remove any now-empty boxes from the list |
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return $box instanceof PackedBox; |
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}); |
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break 2; |
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} |
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} |
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} |
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} while ($iterationSuccessful); |
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//Combine back into a single list |
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$packedBoxes = new PackedBoxList(); |
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$packedBoxes->insertFromArray($boxes); |
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return $packedBoxes; |
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} |
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/** |
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* Attempt to equalise weight distribution between 2 boxes. |
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* |
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* @return bool was the weight rebalanced? |
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*/ |
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private function equaliseWeight(PackedBox &$boxA, PackedBox &$boxB, float $targetWeight): bool |
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{ |
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$anyIterationSuccessful = false; |
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if ($boxA->getWeight() > $boxB->getWeight()) { |
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$overWeightBox = $boxA; |
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$underWeightBox = $boxB; |
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} else { |
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$overWeightBox = $boxB; |
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$underWeightBox = $boxA; |
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} |
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$overWeightBoxItems = $overWeightBox->getItems()->asItemArray(); |
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$underWeightBoxItems = $underWeightBox->getItems()->asItemArray(); |
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foreach ($overWeightBoxItems as $key => $overWeightItem) { |
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if ($overWeightItem->getWeight() + $boxB->getWeight() > $targetWeight) { |
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continue; // moving this item would harm more than help |
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} |
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$newLighterBoxes = $this->doVolumeRepack(array_merge($underWeightBoxItems, [$overWeightItem])); |
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if ($newLighterBoxes->count() !== 1) { |
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continue; //only want to move this item if it still fits in a single box |
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} |
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$underWeightBoxItems[] = $overWeightItem; |
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if (count($overWeightBoxItems) === 1) { //sometimes a repack can be efficient enough to eliminate a box |
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$boxB = $newLighterBoxes->top(); |
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$boxA = null; |
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return true; |
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} else { |
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unset($overWeightBoxItems[$key]); |
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$newHeavierBoxes = $this->doVolumeRepack($overWeightBoxItems); |
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if (count($newHeavierBoxes) !== 1) { |
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continue; |
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} |
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if ($this->didRepackActuallyHelp($boxA, $boxB, $newHeavierBoxes->top(), $newLighterBoxes->top())) { |
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$boxB = $newLighterBoxes->top(); |
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$boxA = $newHeavierBoxes->top(); |
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$anyIterationSuccessful = true; |
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} |
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} |
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} |
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return $anyIterationSuccessful; |
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} |
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/** |
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* Do a volume repack of a set of items. |
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*/ |
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private function doVolumeRepack(iterable $items): PackedBoxList |
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{ |
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$packer = new Packer(); |
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$packer->setBoxes($this->boxes); // use the full set of boxes to allow smaller/larger for full efficiency |
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$packer->setItems($items); |
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return $packer->doVolumePacking(); |
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} |
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/** |
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* Not every attempted repack is actually helpful - sometimes moving an item between two otherwise identical |
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* boxes, or sometimes the box used for the now lighter set of items actually weighs more when empty causing |
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* an increase in total weight. |
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*/ |
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private function didRepackActuallyHelp(PackedBox $oldBoxA, PackedBox $oldBoxB, PackedBox $newBoxA, PackedBox $newBoxB): bool |
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{ |
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$oldList = new PackedBoxList(); |
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$oldList->insertFromArray([$oldBoxA, $oldBoxB]); |
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$newList = new PackedBoxList(); |
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$newList->insertFromArray([$newBoxA, $newBoxB]); |
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return $newList->getWeightVariance() < $oldList->getWeightVariance(); |
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} |
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} |
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dvdoug /
BoxPacker
