83 lines
2.5 KiB
PHP
83 lines
2.5 KiB
PHP
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<?php
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namespace Graphp\Algorithms;
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use Graphp\Algorithms\BaseGraph;
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use Fhaculty\Graph\Exception\UnderflowException;
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use Fhaculty\Graph\Graph;
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use Fhaculty\Graph\Vertex;
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use Fhaculty\Graph\Walk;
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use Fhaculty\Graph\Exception\NegativeCycleException;
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use Graphp\Algorithms\ShortestPath\MooreBellmanFord as SpMooreBellmanFord;
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class DetectNegativeCycle extends BaseGraph
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{
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/**
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* check if the input graph has any negative cycles
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*
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* @return boolean
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* @uses AlgorithmDetectNegativeCycle::getCycleNegative()
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*/
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public function hasCycleNegative()
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{
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try {
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$this->getCycleNegative();
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// cycle was found => okay
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return true;
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// no cycle found
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} catch (UnderflowException $ignore) {}
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return false;
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}
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/**
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* Searches all vertices for the first negative cycle
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*
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* @return Walk
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* @throws UnderflowException if there's no negative cycle
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* @uses AlgorithmSpMooreBellmanFord::getVertices()
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*/
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public function getCycleNegative()
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{
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// remember vertices already visited, as they can not lead to a new cycle
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$verticesVisited = array();
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// check for all vertices
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foreach ($this->graph->getVertices()->getMap() as $vid => $vertex) {
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// skip vertices already visited
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if (!isset($verticesVisited[$vid])) {
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// start MBF algorithm on current vertex
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$alg = new SpMooreBellmanFord($vertex);
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try {
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// try to get all connected vertices (or throw new cycle)
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foreach ($alg->getVertices()->getIds() as $vid) {
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// getting connected vertices succeeded, so skip over all of them
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$verticesVisited[$vid] = true;
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// no cycle found, check next vertex...
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}
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// yey, negative cycle encountered => return
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} catch (NegativeCycleException $e) {
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return $e->getCycle();
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}
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}
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// no more vertices to check => abort
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}
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throw new UnderflowException('No negative cycle found');
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}
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/**
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* create new graph clone with only vertices and edges in negative cycle
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*
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* @return Graph
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* @throws Exception if there's no negative cycle
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* @uses AlgorithmDetectNegativeCycle::getCycleNegative()
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* @uses Walk::createGraph()
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*/
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public function createGraph()
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{
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return $this->getCycleNegative()->createGraph();
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}
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}
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