public static boolean isAcyclic(Digraph digraph) {
int order = digraph.order();
if (order == 0) return true;
Set spanned = new HashSet(order);
DepthFirstStampSearch dfs = new DepthFirstStampSearch(digraph, digraph.vertexIterator().next());
for (Iterator i = digraph.vertexIterator(); i.hasNext(); ) {
Object dfsRoot = i.next();
if (spanned.contains(dfsRoot)) continue;
dfs.reset(dfsRoot);
Map dfsOrders = dfs.traverse(new HashMap(digraph.order()));
for (Iterator j = dfsOrders.entrySet().iterator(); j.hasNext(); ) {
Map.Entry entry = (Map.Entry) j.next();
Object origin = entry.getKey();
DepthFirstStampSearch.OrderPair orgOrders =
(DepthFirstStampSearch.OrderPair) entry.getValue();
spanned.add(origin);
for (ArcIterator k = digraph.outgoingIterator(origin); k.hasNext(); ) {
k.next();
Object dst = k.getDestination();
DepthFirstStampSearch.OrderPair dstOrders =
(DepthFirstStampSearch.OrderPair) dfsOrders.get(dst);
if (dstOrders.getPostOrder() > orgOrders.getPostOrder()) return false;
}
}
if (dfsOrders.size() == order) break;
}
return true;
}
public static Map computeLevels(
Map vertexLevelMap, DigraphIteration digraph, Object root, boolean longest) {
if (vertexLevelMap == null) vertexLevelMap = new HashMap();
MutableInteger rootLevel = (MutableInteger) vertexLevelMap.get(root);
if (rootLevel == null) {
rootLevel = new MutableInteger(0);
vertexLevelMap.put(root, rootLevel);
}
for (ArcIterator i = digraph.outgoingIterator(root); i.hasNext(); ) {
i.next();
Object child = i.getDestination();
int childLevelCandidate = rootLevel.intValue() + 1;
MutableInteger childLevel = (MutableInteger) vertexLevelMap.get(child);
if (childLevel == null) {
childLevel = new MutableInteger(childLevelCandidate);
vertexLevelMap.put(child, childLevel);
computeLevels(vertexLevelMap, digraph, child, longest);
} else if ((longest && childLevel.intValue() < childLevelCandidate)
|| (!longest && childLevel.intValue() > childLevelCandidate)) {
childLevel.setValue(childLevelCandidate);
computeLevels(vertexLevelMap, digraph, child, longest);
}
}
return vertexLevelMap;
}
public static Map shiftLevelsDown(Map vertexLevelMap, DigraphIteration digraph, Object root) {
int minChildLevel = Integer.MAX_VALUE;
for (ArcIterator i = digraph.outgoingIterator(root); i.hasNext(); ) {
i.next();
Object child = i.getDestination();
shiftLevelsDown(vertexLevelMap, digraph, child);
MutableInteger childLevel = (MutableInteger) vertexLevelMap.get(child);
minChildLevel =
(minChildLevel <= childLevel.intValue() ? minChildLevel : childLevel.intValue());
}
if (minChildLevel != Integer.MAX_VALUE) {
MutableInteger rootLevel = (MutableInteger) vertexLevelMap.get(root);
rootLevel.setValue(minChildLevel - 1);
}
return vertexLevelMap;
}