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85 lines
2.3 KiB
PHP
85 lines
2.3 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\Base as Edge;
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use Fhaculty\Graph\Edge\Directed as DirectedEdge;
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use Fhaculty\Graph\Set\Edges;
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use Fhaculty\Graph\Graph;
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use LogicException;
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/**
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* Basic algorithms for working with parallel edges
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*
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* Parallel edges (also called multiple edges or a multi-edge), are two or more
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* edges that are incident to the same two vertices. A simple graph has no
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* multiple edges.
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*
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* @link http://en.wikipedia.org/wiki/Multiple_edges
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*/
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class Parallel extends BaseGraph
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{
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/**
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* checks whether this graph has any parallel edges (aka multigraph)
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*
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* @return boolean
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* @uses Edge::hasEdgeParallel() for every edge
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*/
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public function hasEdgeParallel()
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{
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foreach ($this->graph->getEdges() as $edge) {
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if ($this->hasEdgeParallelEdge($edge)) {
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return true;
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}
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}
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return false;
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}
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/**
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* checks whether this edge has any parallel edges
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*
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* @return boolean
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* @uses Edge::getEdgesParallel()
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*/
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public function hasEdgeParallelEdge(Edge $edge)
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{
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return !$this->getEdgesParallelEdge($edge)->isEmpty();
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}
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/**
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* get set of all Edges parallel to this edge (excluding self)
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*
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* @param Edge $edge
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* @return Edges
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* @throws LogicException
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*/
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public function getEdgesParallelEdge(Edge $edge)
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{
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if ($edge instanceof DirectedEdge) {
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// get all edges between this edge's endpoints
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$edges = $edge->getVertexStart()->getEdgesTo($edge->getVertexEnd())->getVector();
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} else {
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// edge points into both directions (undirected/bidirectional edge)
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// also get all edges in other direction
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$ends = $edge->getVertices();
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$edges = $ends->getVertexFirst()->getEdges()->getEdgesIntersection($ends->getVertexLast()->getEdges())->getVector();
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}
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$pos = array_search($edge, $edges, true);
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if ($pos === false) {
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// @codeCoverageIgnoreStart
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throw new LogicException('Internal error: Current edge not found');
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// @codeCoverageIgnoreEnd
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}
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// exclude current edge from parallel edges
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unset($edges[$pos]);
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return new Edges(array_values($edges));
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}
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}
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