/**
* 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;
}
/**
* Finds source vertices in a Digraph, then enqueues them.
*
* @param Digraph $graph
* @param DepthFirstVisitorInterface $visitor
*
* @return \SplQueue
*/
public static function find_sources(Digraph $graph, DepthFirstVisitorInterface $visitor)
{
$incomings = new \SplObjectStorage();
$queue = new \SplQueue();
foreach ($graph->edges() as $edge) {
if (!isset($incomings[$edge[1]])) {
$incomings[$edge[1]] = new \SplObjectStorage();
}
$incomings[$edge[1]]->attach($edge[0]);
}
// Prime the queue with vertices that have no incoming edges.
foreach ($graph->vertices() as $vertex) {
if (!$incomings->contains($vertex)) {
$queue->push($vertex);
$visitor->onInitializeVertex($vertex, TRUE, $queue);
} else {
$visitor->onInitializeVertex($vertex, FALSE, $queue);
}
}
return $queue;
}
