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<?php declare(strict_types=1); |
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namespace Stratadox\PuzzleSolver\SearchStrategy; |
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use Stratadox\PuzzleSolver\Puzzle; |
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use const INF; |
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/** |
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* Visited Node Cost Checker |
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* |
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* The Visited Node Cost Checker keeps a record of the cost of reaching each |
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* considered candidate. When a candidate is encountered that already has a |
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* recorded cost, the cost of the newly discovered path to reach the same state |
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* as before is compared with the previously recorded cost. If the cost is lower |
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* than before, the record gets updated and the new candidate is considered. In |
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* case the cost is equal or higher than previous paths to the same goal, the |
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* candidate is discarded. |
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* |
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* Decorator for other search strategies. |
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* |
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* @author Stratadox |
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*/ |
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final class VisitedNodeCostChecker implements SearchStrategy |
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{ |
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/** @var float[] */ |
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private $costTowards = []; |
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/** @var SearchStrategy */ |
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private $search; |
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private function __construct(SearchStrategy $search) |
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{ |
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$this->search = $search; |
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} |
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public static function forThe(SearchStrategy $search): self |
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{ |
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return new self($search); |
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} |
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public function isOngoing(): bool |
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{ |
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return $this->search->isOngoing(); |
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} |
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public function consider(Puzzle $puzzle): bool |
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{ |
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$cost = $puzzle->movesSoFar()->cost(); |
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if ($cost < ($this->costTowards[$puzzle->representation()] ?? INF)) { |
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$this->costTowards[$puzzle->representation()] = $cost; |
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return $this->search->consider($puzzle); |
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} |
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return false; |
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} |
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public function nextCandidate(): Puzzle |
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{ |
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return $this->search->nextCandidate(); |
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} |
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} |
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Stratadox /
PuzzleSolver
