/**
* Finds connected components in the provided directed graph.
*
* @param DirectedGraph $graph
* The DirectedGraph to search for connected components.
* @param TarjanSCCVisitor $visitor
* The visitor that will collect and store the connected components. One
* will be created if not provided.
*
* @return TarjanSCCVisitor
* The finalized visitor.
*/
public static function tarjan_scc(DirectedGraph $graph, TarjanSCCVisitor $visitor = NULL)
{
$visitor = $visitor ?: new TarjanSCCVisitor();
$counter = 0;
$stack = array();
$indices = new \SplObjectStorage();
$lowlimits = new \SplObjectStorage();
$visit = function ($vertex) use(&$visit, &$counter, $graph, &$stack, $indices, $lowlimits, $visitor) {
$indices->attach($vertex, $counter);
$lowlimits->attach($vertex, $counter);
$stack[] = $vertex;
$counter++;
$graph->eachAdjacent($vertex, function ($to) use(&$visit, $vertex, $indices, $lowlimits, &$stack) {
if (!$indices->contains($to)) {
$visit($to);
$lowlimits[$vertex] = min($lowlimits[$vertex], $lowlimits[$to]);
} else {
if (in_array($to, $stack)) {
$lowlimits[$vertex] = min($lowlimits[$vertex], $indices[$to]);
}
}
});
if ($lowlimits[$vertex] === $indices[$vertex]) {
$visitor->newComponent();
do {
$other = array_pop($stack);
$visitor->addToCurrentComponent($other);
} while ($other != $vertex);
}
};
$graph->eachVertex(function ($vertex) use(&$visit, $indices) {
if (!$indices->contains($vertex)) {
$visit($vertex);
}
});
return $visitor;
}
/**
* Finds source vertices in a DirectedGraph, then enqueues them.
*
* @param DirectedGraph $graph
* @param DepthFirstVisitorInterface $visitor
*
* @return \SplQueue
*/
public static function find_sources(DirectedGraph $graph, DepthFirstVisitorInterface $visitor)
{
$incomings = new \SplObjectStorage();
$queue = new \SplQueue();
$graph->eachEdge(function ($edge) use(&$incomings) {
if (!isset($incomings[$edge[1]])) {
$incomings[$edge[1]] = new \SplObjectStorage();
}
$incomings[$edge[1]]->attach($edge[0]);
});
// Prime the queue with vertices that have no incoming edges.
$graph->eachVertex(function ($vertex) use($queue, $incomings, $visitor) {
if (!$incomings->contains($vertex)) {
$queue->push($vertex);
// TRUE second param indicates source vertex
$visitor->onInitializeVertex($vertex, TRUE, $queue);
} else {
$visitor->onInitializeVertex($vertex, FALSE, $queue);
}
});
return $queue;
}
