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45 lines
1.3 KiB
PHP
45 lines
1.3 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\Edge\Directed as EdgeDirected;
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use Fhaculty\Graph\Graph;
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use Fhaculty\Graph\Vertex;
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/**
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* Basic algorithms for working with symmetric digraphs
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*
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* A directed graph is called symmetric if, for every arc that belongs to it,
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* the corresponding reversed arc (antiparallel directed edge) also belongs to it.
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*
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* @link http://en.wikipedia.org/wiki/Directed_graph#Classes_of_digraphs
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*/
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class Symmetric extends BaseGraph
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{
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/**
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* checks whether this graph is symmetric (for every edge a->b there's also an edge b->a)
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*
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* @return boolean
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* @uses Graph::getEdges()
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* @uses EdgeDirected::getVertexStart()
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* @uses EdgeDirected::getVertedEnd()
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* @uses Vertex::hasEdgeTo()
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*/
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public function isSymmetric()
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{
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// check all edges
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foreach ($this->graph->getEdges() as $edge) {
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// only check directed edges (undirected ones are symmetric by definition)
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if ($edge instanceof EdgeDirected) {
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// check if end also has an edge to start
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if (!$edge->getVertexEnd()->hasEdgeTo($edge->getVertexStart())) {
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return false;
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}
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}
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}
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return true;
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}
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}
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