public List<Group> buildGroupsDirected() {
List<Group> groups = new LinkedList<>();
// First determine 'start' relations, i.e. relations without incoming
// edges in the relation graph
TLongSet starts = new TLongHashSet();
Collection<Long> ids = graph.getNodes();
for (long id : ids) {
if (graph.getEdgesIn(id).isEmpty()) {
starts.add(id);
}
}
// Build sub-graphs reachable from 'start' relations
logger.debug("Number of start relations: " + starts.size());
for (long start : starts.toArray()) {
groups.add(build(start));
}
// In case of circles within the relation graph that are not reachable
// from any start relation, there may be some relations left, that have
// not been put into groups yet.
TLongSet remaining = new TLongHashSet();
remaining.addAll(ids);
for (Group group : groups) {
remaining.removeAll(group.getRelationIds());
}
if (remaining.size() > 0) {
logger.debug("remaining: " + remaining.size());
while (!remaining.isEmpty()) {
long id = any(remaining);
TLongSet reachable = reachable(graph, id);
remaining.removeAll(reachable);
long lowest = IdUtil.lowestId(reachable);
groups.add(new Group(lowest, reachable));
}
}
return groups;
}
public List<Group> buildGroupsUndirected() {
List<Group> groups = new LinkedList<>();
TLongSet nodes = new TLongHashSet(graph.getNodes());
while (!nodes.isEmpty()) {
long id = any(nodes);
TLongSet reachable = reachable(graph, id);
nodes.removeAll(reachable);
groups.add(new Group(id, reachable));
}
return groups;
}