/** {@inheritDoc} */
protected void encounterVertexAgain(V vertex, E edge) {
super.encounterVertexAgain(vertex, edge);
int i;
if (root != null) {
// For rooted detection, the path must either
// double back to the root, or to a node of a cycle
// which has already been detected.
if (vertex.equals(root)) {
i = 0;
} else if ((cycleSet != null) && cycleSet.contains(vertex)) {
i = 0;
} else {
return;
}
} else {
i = path.indexOf(vertex);
}
if (i > -1) {
if (cycleSet == null) {
// we're doing yes/no cycle detection
throw new CycleDetectedException();
} else {
for (; i < path.size(); ++i) {
cycleSet.add(path.get(i));
}
}
}
}
/**
* Finds the vertex set for the subgraph of all cycles.
*
* @return set of all vertices which participate in at least one cycle in this graph
*/
public Set<V> findCycles() {
// ProbeIterator can't be used to handle this case,
// so use StrongConnectivityInspector instead.
StrongConnectivityInspector<V, E> inspector = new StrongConnectivityInspector<V, E>(graph);
List<Set<V>> components = inspector.stronglyConnectedSets();
// A vertex participates in a cycle if either of the following is
// true: (a) it is in a component whose size is greater than 1
// or (b) it is a self-loop
Set<V> set = new HashSet<V>();
for (Set<V> component : components) {
if (component.size() > 1) {
// cycle
set.addAll(component);
} else {
V v = component.iterator().next();
if (graph.containsEdge(v, v)) {
// self-loop
set.add(v);
}
}
}
return set;
}