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/* ==========================================
* 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.
*/
/* -------------------------
* KShortestPaths.java
* -------------------------
* (C) Copyright 2007-2007, by France Telecom
*
* Original Author: Guillaume Boulmier and Contributors.
* Contributor(s): John V. Sichi
*
* $Id: KShortestPaths.java 586 2008-01-27 23:30:50Z perfecthash $
*
* Changes
* -------
* 05-Jun-2007 : Initial revision (GB);
* 05-Jul-2007 : Added support for generics (JVS);
*
*/
package org.jgrapht.alg;
import java.util.*;
import org.jgrapht.*;
/**
* The algorithm determines the k shortest simple paths in increasing order of
* weight. Weights could be negative (but no negative cycle is allowed), paths
* could be constrained by a maximum number of edges.
*
* @author Guillaume Boulmier
* @since July 5, 2007
*/
public class KShortestPaths
{
// ~ Instance fields
// --------------------------------------------------------
//~ Instance fields --------------------------------------------------------
/**
* Graph on which shortest paths are searched.
*/
private Graph graph;
private int nMaxHops;
private int nPaths;
private V startVertex;
//~ Constructors -----------------------------------------------------------
// ~ Constructors
// -----------------------------------------------------------
/**
* Creates an object to compute ranking shortest paths between the start
* vertex and others vertices.
*
* @param graph
* @param startVertex
* @param k number of paths to be computed.
*/
public KShortestPaths(Graph graph, V startVertex, int k)
{
this(graph, startVertex, k, graph.vertexSet().size() - 1);
}
/**
* Creates an object to calculate ranking shortest paths between the start
* vertex and others vertices.
*
* @param graph graph on which shortest paths are searched.
* @param startVertex start vertex of the calculated paths.
* @param nPaths number of ranking paths between the start vertex and an end
* vertex.
* @param nMaxHops maximum number of edges of the calculated paths.
*
* @throws NullPointerException if the specified graph or startVertex is
* null.
* @throws IllegalArgumentException if nPaths is negative or 0.
* @throws IllegalArgumentException if nMaxHops is negative or 0.
*/
public KShortestPaths(
Graph graph,
V startVertex,
int nPaths,
int nMaxHops)
{
assertKShortestPathsFinder(graph, startVertex, nPaths, nMaxHops);
this.graph = graph;
this.startVertex = startVertex;
this.nPaths = nPaths;
this.nMaxHops = nMaxHops;
}
//~ Methods ----------------------------------------------------------------
// ~ Methods
// ----------------------------------------------------------------
/**
* Returns the k shortest simple paths in increasing order of weight.
* Running time : O(k*m*n) where m is the number of edges.
*
* @param endVertex target vertex of the calculated paths.
*
* @return list of paths, or null if no path exists between the
* start vertex and the end vertex.
*/
public List> getPaths(V endVertex)
{
assertGetPaths(endVertex);
KShortestPathsIterator iter =
new KShortestPathsIterator(
this.graph,
this.startVertex,
endVertex,
this.nPaths);
// at the i-th pass the shortest paths with less (or equal) than i edges
// are calculated.
for (
int passNumber = 1;
(passNumber <= this.nMaxHops)
&& iter.hasNext();
passNumber++)
{
iter.next();
}
List> list = iter.getPathElements(endVertex);
if (list == null) {
return null;
}
List> pathList = new ArrayList>();
for (RankingPathElement element : list) {
pathList.add(new PathWrapper(element));
}
return pathList;
}
private void assertGetPaths(V endVertex)
{
if (endVertex == null) {
throw new NullPointerException("endVertex is null");
}
if (endVertex.equals(this.startVertex)) {
throw new IllegalArgumentException(
"The end vertex is the same as the start vertex!");
}
if (!this.graph.vertexSet().contains(endVertex)) {
throw new IllegalArgumentException(
"Graph must contain the end vertex!");
}
}
private void assertKShortestPathsFinder(
Graph graph,
V startVertex,
int nPaths,
int nMaxHops)
{
if (graph == null) {
throw new NullPointerException("graph is null");
}
if (startVertex == null) {
throw new NullPointerException("startVertex is null");
}
if (nPaths <= 0) {
throw new NullPointerException("nPaths is negative or 0");
}
if (nMaxHops <= 0) {
throw new NullPointerException("nMaxHops is negative or 0");
}
}
//~ Inner Classes ----------------------------------------------------------
private class PathWrapper
implements GraphPath
{
private RankingPathElement rankingPathElement;
private List edgeList;
PathWrapper(RankingPathElement rankingPathElement)
{
this.rankingPathElement = rankingPathElement;
}
// implement GraphPath
public Graph getGraph()
{
return graph;
}
// implement GraphPath
public V getStartVertex()
{
return startVertex;
}
// implement GraphPath
public V getEndVertex()
{
return rankingPathElement.getVertex();
}
// implement GraphPath
public List getEdgeList()
{
if (edgeList == null) {
edgeList = rankingPathElement.createEdgeListPath();
}
return edgeList;
}
// implement GraphPath
public double getWeight()
{
return rankingPathElement.getWeight();
}
}
}
// End KShortestPaths.java