public function kruskal()
{
$ufds = new UFDS();
$edgeQ = $this->edgeList;
$akeys = array_keys($this->adjList);
for ($i = 0; $i < count($akeys); $i++) {
$ufds->insert($akeys[$i]);
}
$edgeSet = array();
usort($edgeQ, 'tripleSort');
//by weight
if (!$this->min) {
$edgeQ = array_reverse($edgeQ);
}
$length = count($edgeQ);
for ($i = 0; $i < $length; $i++) {
$e = array_shift($edgeQ);
if (!$ufds->isSameSet($e->from(), $e->to())) {
//if does not form cycle
$edgeSet[] = $e;
$ufds->unionSet($e->from(), $e->to());
}
}
return $edgeSet;
}
