org.jgrapht.traverse.CrossComponentIterator Maven / Gradle / Ivy
/*
* (C) Copyright 2003-2021, by Barak Naveh and Contributors.
*
* JGraphT : a free Java graph-theory library
*
* See the CONTRIBUTORS.md file distributed with this work for additional
* information regarding copyright ownership.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License 2.0 which is available at
* http://www.eclipse.org/legal/epl-2.0, or the
* GNU Lesser General Public License v2.1 or later
* which is available at
* http://www.gnu.org/licenses/old-licenses/lgpl-2.1-standalone.html.
*
* SPDX-License-Identifier: EPL-2.0 OR LGPL-2.1-or-later
*/
package org.jgrapht.traverse;
import org.jgrapht.*;
import org.jgrapht.event.*;
import java.util.*;
/**
* Provides a cross-connected-component traversal functionality for iterator subclasses.
*
* @param vertex type
* @param edge type
* @param type of data associated to seen vertices
*
* @author Barak Naveh
*/
public abstract class CrossComponentIterator
extends
AbstractGraphIterator
{
private static final int CCS_BEFORE_COMPONENT = 1;
private static final int CCS_WITHIN_COMPONENT = 2;
private static final int CCS_AFTER_COMPONENT = 3;
private final ConnectedComponentTraversalEvent ccFinishedEvent =
new ConnectedComponentTraversalEvent(
this, ConnectedComponentTraversalEvent.CONNECTED_COMPONENT_FINISHED);
private final ConnectedComponentTraversalEvent ccStartedEvent =
new ConnectedComponentTraversalEvent(
this, ConnectedComponentTraversalEvent.CONNECTED_COMPONENT_STARTED);
/**
* Stores the vertices that have been seen during iteration and (optionally) some additional
* traversal info regarding each vertex.
*/
private Map seen = new HashMap<>();
/**
* Iterator which provides start vertices for cross-component iteration.
*/
private Iterator entireGraphVertexIterator = null;
/**
* Iterator which provides start vertices for specified start vertices.
*/
private Iterator startVertexIterator = null;
/**
* The current vertex.
*/
private V startVertex;
/**
* The connected component state
*/
private int state = CCS_BEFORE_COMPONENT;
/**
* Creates a new iterator for the specified graph.
*
* @param g the graph to be iterated
*/
public CrossComponentIterator(Graph g)
{
this(g, (V) null);
}
/**
* Creates a new iterator for the specified graph. Iteration will start at the specified start
* vertex. If the specified start vertex is
* null, Iteration will start at an arbitrary graph vertex.
*
* @param g the graph to be iterated.
* @param startVertex the vertex iteration to be started.
*
* @throws IllegalArgumentException if g==null or does not contain
* startVertex
*/
public CrossComponentIterator(Graph g, V startVertex)
{
this(g, startVertex == null ? null : Collections.singletonList(startVertex));
}
/**
* Creates a new iterator for the specified graph. Iteration will start at the specified start
* vertices. If the specified start vertices is
* null, Iteration will start at an arbitrary graph vertex.
*
* @param g the graph to be iterated.
* @param startVertices the vertices iteration to be started.
*
* @throws IllegalArgumentException if g==null or does not contain
* startVertex
*/
public CrossComponentIterator(Graph g, Iterable startVertices)
{
super(g);
/*
* Initialize crossComponentTraversal and test for containment
*/
if (startVertices == null) {
this.crossComponentTraversal = true;
} else {
this.crossComponentTraversal = false;
this.startVertexIterator = startVertices.iterator();
}
/*
* Initialize start vertex
*/
Iterator it =
crossComponentTraversal ? getEntireGraphVertexIterator() : startVertexIterator;
// pick a start vertex if possible
if (it.hasNext()) {
this.startVertex = it.next();
if (!graph.containsVertex(startVertex)) {
throw new IllegalArgumentException("graph must contain the start vertex");
}
} else {
this.startVertex = null;
}
}
@Override
public boolean hasNext()
{
if (startVertex != null) {
encounterStartVertex();
}
if (isConnectedComponentExhausted()) {
if (state == CCS_WITHIN_COMPONENT) {
state = CCS_AFTER_COMPONENT;
if (nListeners != 0) {
fireConnectedComponentFinished(ccFinishedEvent);
}
}
Iterator it =
isCrossComponentTraversal() ? getEntireGraphVertexIterator() : startVertexIterator;
while (it != null && it.hasNext()) {
V v = it.next();
if (!graph.containsVertex(v)) {
throw new IllegalArgumentException("graph must contain the start vertex");
}
if (!isSeenVertex(v)) {
encounterVertex(v, null);
state = CCS_BEFORE_COMPONENT;
return true;
}
}
return false;
} else {
return true;
}
}
@Override
public V next()
{
if (startVertex != null) {
encounterStartVertex();
}
if (hasNext()) {
if (state == CCS_BEFORE_COMPONENT) {
state = CCS_WITHIN_COMPONENT;
if (nListeners != 0) {
fireConnectedComponentStarted(ccStartedEvent);
}
}
V nextVertex = provideNextVertex();
if (nListeners != 0) {
fireVertexTraversed(createVertexTraversalEvent(nextVertex));
}
addUnseenChildrenOf(nextVertex);
return nextVertex;
} else {
throw new NoSuchElementException();
}
}
/**
* Lazily instantiates {@code entireGraphVertexIterator}.
*
* @return iterator which provides start vertices for cross-component iteration
*/
protected Iterator getEntireGraphVertexIterator()
{
if (entireGraphVertexIterator == null) {
assert (isCrossComponentTraversal());
entireGraphVertexIterator = graph.vertexSet().iterator();
}
return entireGraphVertexIterator;
}
/**
* Returns true if there are no more uniterated vertices in the currently iterated
* connected component; false otherwise.
*
* @return true if there are no more uniterated vertices in the currently iterated
* connected component; false otherwise.
*/
protected abstract boolean isConnectedComponentExhausted();
/**
* Update data structures the first time we see a vertex.
*
* @param vertex the vertex encountered
* @param edge the edge via which the vertex was encountered, or null if the vertex is a
* starting point
*/
protected abstract void encounterVertex(V vertex, E edge);
/**
* Returns the vertex to be returned in the following call to the iterator next
* method.
*
* @return the next vertex to be returned by this iterator.
*/
protected abstract V provideNextVertex();
/**
* Access the data stored for a seen vertex.
*
* @param vertex a vertex which has already been seen.
*
* @return data associated with the seen vertex or null if no data was associated
* with the vertex. A null return can also indicate that the vertex was
* explicitly associated with
* null.
*/
protected D getSeenData(V vertex)
{
return seen.get(vertex);
}
/**
* Determines whether a vertex has been seen yet by this traversal.
*
* @param vertex vertex in question
*
* @return true if vertex has already been seen
*/
protected boolean isSeenVertex(V vertex)
{
return seen.containsKey(vertex);
}
/**
* Called whenever we re-encounter a vertex. The default implementation does nothing.
*
* @param vertex the vertex re-encountered
* @param edge the edge via which the vertex was re-encountered
*/
protected abstract void encounterVertexAgain(V vertex, E edge);
/**
* Stores iterator-dependent data for a vertex that has been seen.
*
* @param vertex a vertex which has been seen.
* @param data data to be associated with the seen vertex.
*
* @return previous value associated with specified vertex or
* null if no data was associated with the vertex. A
* null return can also indicate that the vertex was explicitly associated with
* null.
*/
protected D putSeenData(V vertex, D data)
{
return seen.put(vertex, data);
}
/**
* Called when a vertex has been finished (meaning is dependent on traversal represented by
* subclass).
*
* @param vertex vertex which has been finished
*/
protected void finishVertex(V vertex)
{
if (nListeners != 0) {
fireVertexFinished(createVertexTraversalEvent(vertex));
}
}
/**
* Selects the outgoing edges for a given vertex based on the source vertex and other traversal
* state. The default implementation returns all outgoing edges.
*
* @param vertex vertex in question
* @return set of outgoing edges connected to the vertex
*/
protected Set selectOutgoingEdges(V vertex)
{
return graph.outgoingEdgesOf(vertex);
}
private void addUnseenChildrenOf(V vertex)
{
for (E edge : selectOutgoingEdges(vertex)) {
if (nListeners != 0) {
fireEdgeTraversed(createEdgeTraversalEvent(edge));
}
V oppositeV = Graphs.getOppositeVertex(graph, edge, vertex);
if (isSeenVertex(oppositeV)) {
encounterVertexAgain(oppositeV, edge);
} else {
encounterVertex(oppositeV, edge);
}
}
}
private void encounterStartVertex()
{
encounterVertex(startVertex, null);
startVertex = null;
}
}