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<?php declare(strict_types=1); |
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namespace Stratadox\Pathfinder; |
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use const INF; |
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use SplPriorityQueue; |
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use Stratadox\Pathfinder\Reconstruction\PathRetracer; |
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final class SingleDijkstraPathfinder implements SinglePathfinder |
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{ |
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private $network; |
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private $path; |
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private function __construct(Network $network) |
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{ |
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$this->network = $network; |
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$this->path = new PathRetracer(); |
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} |
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public static function operatingIn(Network $graph): SinglePathfinder |
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{ |
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return new self($graph); |
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} |
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public function between(string $start, string $goal): array |
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{ |
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if (!$this->network->has($start)) { |
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throw NonExistingStart::tried($start); |
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} |
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$distanceTo = [$start => 0]; |
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$lastStepBefore = []; |
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$underConsideration = new SplPriorityQueue(); |
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$underConsideration->insert($start, 0); |
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while (!$underConsideration->isEmpty()) { |
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$node = $underConsideration->top(); |
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$underConsideration->next(); |
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if ($goal === $node) { |
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return $this->path->retrace($start, $goal, $lastStepBefore); |
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} |
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foreach ($this->network->neighboursOf($node) as $neighbour) { |
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$alternativeCost = ($distanceTo[$node] ?? INF) + |
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$this->network->movementCostBetween($node, $neighbour); |
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if ($alternativeCost < ($distanceTo[$neighbour] ?? INF)) { |
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$distanceTo[$neighbour] = $alternativeCost; |
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$lastStepBefore[$neighbour] = $node; |
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$underConsideration->insert($neighbour, -$alternativeCost); |
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} |
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} |
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} |
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throw NoSuchPath::between($start, $goal); |
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} |
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} |
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Stratadox /
Pathfinder
