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66 lines
1.9 KiB
PHP
66 lines
1.9 KiB
PHP
<?php
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namespace Graphp\Algorithms;
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use Graphp\Algorithms\BaseGraph;
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use Fhaculty\Graph\Exception\UnexpectedValueException;
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use Fhaculty\Graph\Vertex;
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use Fhaculty\Graph\Set\Vertices;
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use Fhaculty\Graph\Graph;
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/**
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* topological sorting / order, also known as toposort / topsort, commonly used in resolving dependencies
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*
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* @author clue
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* @link http://en.wikipedia.org/wiki/Topological_sorting
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*/
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class TopologicalSort extends BaseGraph
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{
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/**
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* run algorithm and return an ordered/sorted set of Vertices
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*
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* the topologic sorting may be non-unique depending on your edges. this
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* algorithm tries to keep the order of vertices as added to the graph in
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* this case.
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*
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* @return Vertices
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*/
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public function getVertices()
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{
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$tsl = array();
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$visited = array();
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// TODO: find alternative to recursive algorithm to avoid hitting recursion limit with ~100 nodes
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// TODO: avoid having to reverse all vertices multiple times
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foreach(array_reverse($this->graph->getVertices()->getVector()) as $vertex) {
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$this->visit($vertex, $visited, $tsl);
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}
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return new Vertices(array_reverse($tsl, true));
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}
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protected function visit(Vertex $vertex, array &$visited, array &$tsl)
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{
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$vid = $vertex->getId();
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if (isset($visited[$vid])) {
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if ($visited[$vid] === false) {
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// temporary mark => not a DAG
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throw new UnexpectedValueException('Not a DAG');
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}
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// otherwise already marked/visisted => no need to check again
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} else {
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// temporary mark
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$visited[$vid] = false;
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foreach (array_reverse($vertex->getVerticesEdgeTo()->getVector()) as $v) {
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$this->visit($v, $visited, $tsl);
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}
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// mark as visited and include in result
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$visited[$vid] = true;
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$tsl[$vid] = $vertex;
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}
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}
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}
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