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<?php declare(strict_types=1); |
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namespace Stratadox\PuzzleSolver\SearchStrategy; |
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use SplPriorityQueue; |
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use Stratadox\PuzzleSolver\Heuristic; |
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use Stratadox\PuzzleSolver\Puzzle; |
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use Stratadox\PuzzleSolver\Moves; |
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/** |
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* Best-first search strategy |
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* |
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* Best-first searches enqueue newly encountered nodes by order of quality. The |
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* move that is most likely to lead to the desired outcome is considered first. |
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* |
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* @author Stratadox |
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*/ |
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final class BestFirstStrategy implements SearchStrategy |
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{ |
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/** @var SplPriorityQueue */ |
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private $queue; |
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/** @var Puzzle */ |
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private $originalPuzzle; |
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/** @var Heuristic */ |
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private $heuristic; |
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private function __construct( |
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SplPriorityQueue $queue, |
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Puzzle $originalPuzzle, |
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Heuristic $heuristic |
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) { |
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$this->queue = $queue; |
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$this->originalPuzzle = $originalPuzzle; |
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$this->heuristic = $heuristic; |
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} |
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public static function withHeuristic( |
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Heuristic $heuristic, |
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Puzzle $puzzle |
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): SearchStrategy { |
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$queue = new SplPriorityQueue(); |
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$queue->insert(Moves::none(), 0); // @todo heuristic |
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return new self($queue, $puzzle, $heuristic); |
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} |
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public function isOngoing(): bool |
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{ |
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return !$this->queue->isEmpty(); |
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} |
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public function consider(Puzzle $puzzle): bool |
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{ |
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$this->insert($puzzle->movesSoFar(), $this->heuristic->estimate($puzzle)); |
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return true; |
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} |
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public function nextCandidate(): Puzzle |
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{ |
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return $this->originalPuzzle->afterMaking(...$this->queue->extract()); |
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} |
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private function insert(Moves $moves, float $heuristic): void |
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{ |
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$this->queue->insert($moves, -($moves->cost() + $heuristic)); |
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} |
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} |
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Stratadox /
PuzzleSolver
