public static boolean isTree(Digraph digraph) {
Object root = null;
for (Iterator i = digraph.vertexIterator(); i.hasNext(); ) {
Object vertex = i.next();
int inSize = digraph.incomingSize(vertex);
if (inSize == 0) {
root = vertex;
break;
}
}
// not a tree - no vertex with 0 in-degree
if (root == null) return false;
// try to reach all vertices from the root candidate
BreadthFirstSearch traversal = new BreadthFirstSearch(digraph, root);
while (traversal.isValidTree() && traversal.hasNext()) traversal.next();
// not a tree - one of vertices has been seen more than once by the BFS
if (!traversal.isValidTree()) return false;
// has every vertex been reached?
Set seenVertices = traversal.getSeenVertices();
for (Iterator i = digraph.vertexIterator(); i.hasNext(); )
if (!seenVertices.contains(i.next())) return false;
// all tests are passed - good!
return true;
}
public static Map shiftLevelsDown(Map vertexLevelMap, Digraph digraph) {
for (Iterator i = digraph.vertexIterator(); i.hasNext(); ) {
Object rootCandidate = i.next();
if (digraph.incomingSize(rootCandidate) == 0)
shiftLevelsDown(vertexLevelMap, digraph, rootCandidate);
}
return vertexLevelMap;
}
public static Map computeLevels(Map vertexLevelMap, Digraph digraph, boolean longest) {
if (vertexLevelMap == null) vertexLevelMap = new HashMap(digraph.order());
for (Iterator i = digraph.vertexIterator(); i.hasNext(); ) {
Object rootCandidate = i.next();
if (digraph.incomingSize(rootCandidate) == 0)
computeLevels(vertexLevelMap, digraph, rootCandidate, longest);
}
return vertexLevelMap;
}