/**
* Recursive part of tarjans algorithm to find strongly connected components. Algorithm is e.g.
* described in <a
* href="http://en.wikipedia.org/wiki/Tarjan's_strongly_connected_components_algorithm">wikipedia</a>
*
* @param maxdfs The current value for maxdfs.
* @param v The current Node to process.
* @param workset Set of all unreached Nodes.
* @param stack Temporary datastructure for algorithm.
* @param nodeStrMap Because the sccs are returned as a list of variables (i.e. Strings), the
* mapping from Node to String must be given.
* @param sccs All found strongly connected components are added to this list.
* @return an updated value for maxdfs.
*/
private static int tarjan(
int maxdfs,
DirectedGraph.Node v,
Set<DirectedGraph.Node> workset,
LinkedList<DirectedGraph.Node> stack,
Map<DirectedGraph.Node, String> nodeStrMap,
List<List<String>> sccs) {
v.dfs = maxdfs;
v.lowlink = maxdfs;
maxdfs++;
stack.push(v);
workset.remove(v);
for (DirectedGraph.Node succ : v.getSuccessors()) {
if (workset.contains(succ)) {
maxdfs = tarjan(maxdfs, succ, workset, stack, nodeStrMap, sccs);
v.lowlink = Math.min(v.lowlink, succ.lowlink);
} else if (succ.dfs > 0) { // <==> stack.contains(succ)
v.lowlink = Math.min(v.lowlink, succ.dfs);
}
}
if (v.lowlink == v.dfs) {
DirectedGraph.Node succ;
LinkedList<String> scc = new LinkedList<>();
do {
succ = stack.pop();
succ.dfs = -succ.dfs;
scc.add(nodeStrMap.get(succ));
} while (!succ.equals(v));
if (scc.size() > 1) {
sccs.add(scc);
}
}
return maxdfs;
}
