/**
* The function finds out the lowest common ancestor(LCA) of two nodes.
* 1
* / \
* 2 5
* / \ \
* 3 4 6
* For example: LCA of (3,4) would be 2
* LCA of (3,6) would be 1.
* @param Vertex $local
* @param Vertex $remote
* @return Lowest common ancestor from the graph.
*/
public function find(Vertex $local, Vertex $remote)
{
// Traverse in reverse order starting from $local to the root.
$direction = BreadthFirst::DIRECTION_REVERSE;
// Use BFS algorithm to get all vertices starting with $local to the root.
$bfs_local = new BreadthFirst($local);
$vertices_local = $bfs_local->setDirection($direction)->getVertices();
// Use BFS algorithm to get all vertices starting with $remote to the root.
$bfs_remote = new BreadthFirst($remote);
$vertices_remote = $bfs_remote->setDirection($direction)->getVertices();
// Intersect the $vertices_local and $vertices_remote to get all common
// ancestors for $local and $remote. If the $vertices_intersection array is
// not empty then first value should be our solution - the LCA.
$vertices_intersection = $vertices_local->getVerticesIntersection($vertices_remote)->getMap();
if ($lca = reset($vertices_intersection)) {
return $lca;
} else {
throw new LcaException("No common ancestor found");
}
}
/**
*
* @param Vertex $vertex
* @return SearchBreadthFirst
*/
private function createSearch(Vertex $vertex)
{
$alg = new SearchBreadthFirst($vertex);
// follow into both directions (loosely connected)
return $alg->setDirection(SearchBreadthFirst::DIRECTION_BOTH);
}
