/* ==========================================
* JGraphT : a free Java graph-theory library
* ==========================================
*
* Project Info: http://jgrapht.sourceforge.net/
* Project Creator: Barak Naveh (http://sourceforge.net/users/barak_naveh)
*
* (C) Copyright 2003-2007, by Barak Naveh and Contributors.
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; if not, write to the Free Software Foundation,
* Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
*/
/* -----------------------
* DepthFirstIterator.java
* -----------------------
* (C) Copyright 2003-2007, by Liviu Rau and Contributors.
*
* Original Author: Liviu Rau
* Contributor(s): Barak Naveh
* Christian Hammer
*
* $Id: DepthFirstIterator.java 568 2007-09-30 00:12:18Z perfecthash $
*
* Changes
* -------
* 29-Jul-2003 : Initial revision (LR);
* 31-Jul-2003 : Fixed traversal across connected components (BN);
* 06-Aug-2003 : Extracted common logic to TraverseUtils.XXFirstIterator (BN);
* 31-Jan-2004 : Reparented and changed interface to parent class (BN);
* 04-May-2004 : Made generic (CH)
*
*/
package org.jgrapht.traverse;
import java.util.*;
import org.jgrapht.*;
/**
* A depth-first iterator for a directed and an undirected graph. For this
* iterator to work correctly the graph must not be modified during iteration.
* Currently there are no means to ensure that, nor to fail-fast. The results of
* such modifications are undefined.
*
* @author Liviu Rau
* @author Barak Naveh
* @since Jul 29, 2003
*/
public class DepthFirstIterator<V, E>
extends CrossComponentIterator<V, E, CrossComponentIterator.VisitColor>
{
//~ Instance fields --------------------------------------------------------
/**
* LIFO stack of vertices which have been encountered but not yet visited
* (WHITE). This stack also contains <em>sentinel</em> entries representing
* vertices which have been visited but are still GRAY. A sentinel entry is
* a sequence (v, null), whereas a non-sentinel entry is just (v).
*/
private List<V> stack = new ArrayList<V>();
//~ Constructors -----------------------------------------------------------
/**
* Creates a new depth-first iterator for the specified graph.
*
* @param g the graph to be iterated.
*/
public DepthFirstIterator(Graph<V, E> g)
{
this(g, null);
}
/**
* Creates a new depth-first iterator for the specified graph. Iteration
* will start at the specified start vertex and will be limited to the
* connected component that includes that vertex. If the specified start
* vertex is <code>null</code>, iteration will start at an arbitrary vertex
* and will not be limited, that is, will be able to traverse all the graph.
*
* @param g the graph to be iterated.
* @param startVertex the vertex iteration to be started.
*/
public DepthFirstIterator(Graph<V, E> g, V startVertex)
{
super(g, startVertex);
}
//~ Methods ----------------------------------------------------------------
/**
* @see CrossComponentIterator#isConnectedComponentExhausted()
*/
protected boolean isConnectedComponentExhausted()
{
for (;;) {
if (stack.isEmpty()) {
return true;
}
if (peekStack() != null) {
// Found a non-sentinel.
return false;
}
// Found a sentinel: pop it, record the finish time,
// and then loop to check the rest of the stack.
// Pop null we peeked at above.
popStack();
// This will pop corresponding vertex to be recorded as finished.
recordFinish();
}
}
/**
* @see CrossComponentIterator#encounterVertex(Object, Object)
*/
protected void encounterVertex(V vertex, E edge)
{
putSeenData(vertex, VisitColor.WHITE);
stack.add(vertex);
}
/**
* @see CrossComponentIterator#encounterVertexAgain(Object, Object)
*/
protected void encounterVertexAgain(V vertex, E edge)
{
VisitColor color = getSeenData(vertex);
if (color != VisitColor.WHITE) {
// We've already visited this vertex; no need to mess with the
// stack (either it's BLACK and not there at all, or it's GRAY
// and therefore just a sentinel).
return;
}
int i = stack.indexOf(vertex);
// Since we've encountered it before, and it's still WHITE, it
// *must* be on the stack.
assert (i > -1);
stack.remove(i);
stack.add(vertex);
}
/**
* @see CrossComponentIterator#provideNextVertex()
*/
protected V provideNextVertex()
{
V v;
for (;;) {
v = popStack();
if (v == null) {
// This is a finish-time sentinel we previously pushed.
recordFinish();
// Now carry on with another pop until we find a non-sentinel
} else {
// Got a real vertex to start working on
break;
}
}
// Push a sentinel for v onto the stack so that we'll know
// when we're done with it.
stack.add(v);
stack.add(null);
putSeenData(v, VisitColor.GRAY);
return v;
}
private V popStack()
{
return stack.remove(stack.size() - 1);
}
private V peekStack()
{
return stack.get(stack.size() - 1);
}
private void recordFinish()
{
V v = popStack();
putSeenData(v, VisitColor.BLACK);
finishVertex(v);
}
}
// End DepthFirstIterator.java