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DijkstraShortestPath.java

/* ==========================================
 * JGraphT : a free Java graph-theory library
 * ==========================================
 *
 * Project Info:  http://jgrapht.sourceforge.net/
 * Project Lead:  Barak Naveh (http://sourceforge.net/users/barak_naveh)
 *
 * (C) Copyright 2003-2004, 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.
 */
/* -------------------------
 * DijkstraShortestPath.java
 * -------------------------
 * (C) Copyright 2003, by John V. Sichi and Contributors.
 *
 * Original Author:  John V. Sichi
 *
 * $Id: DijkstraShortestPath.java,v 1.3 2005/05/30 05:37:28 perfecthash Exp $
 *
 * Changes
 * -------
 * 02-Sep-2003 : Initial revision (JVS);
 * 29-May-2005 : Make non-static and add radius support (JVS);
 *
 */
package org._3pq.jgrapht.alg;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org._3pq.jgrapht.Edge;
import org._3pq.jgrapht.Graph;
import org._3pq.jgrapht.traverse.ClosestFirstIterator;

/**
 * An implementation of <a
 * href="http://mathworld.wolfram.com/DijkstrasAlgorithm.html"> Dijkstra's
 * shortest path algorithm</a> using <code>ClosestFirstIterator</code>.
 *
 * @author John V. Sichi
 *
 * @since Sep 2, 2003
 */
00058 public final class DijkstraShortestPath {
    private List   m_edgeList;
    private double m_pathLength;

    /**
     * Creates and executes a new DijkstraShortestPath algorithm instance. An
     * instance is only good for a single search; after construction, it can
     * be accessed to retrieve information about the path found.
     *
     * @param graph the graph to be searched
     * @param startVertex the vertex at which the path should start
     * @param endVertex the vertex at which the path should end
     * @param radius limit on path length, or Double.POSITIVE_INFINITY for
     *        unbounded search
     */
00073     public DijkstraShortestPath( Graph graph, Object startVertex,
        Object endVertex, double radius ) {
        ClosestFirstIterator iter =
            new ClosestFirstIterator( graph, startVertex, radius );

        while( iter.hasNext(  ) ) {
            Object vertex = iter.next(  );

            if( vertex.equals( endVertex ) ) {
                createEdgeList( iter, endVertex );
                m_pathLength = iter.getShortestPathLength( endVertex );

                return;
            }
        }

        m_edgeList       = null;
        m_pathLength     = Double.POSITIVE_INFINITY;
    }

    /**
     * Return the edges making up the path found.
     *
     * @return List of Edges, or null if no path exists
     */
00098     public List getPathEdgeList(  ) {
        return m_edgeList;
    }


    /**
     * Return the length of the path found.
     *
     * @return path length, or Double.POSITIVE_INFINITY if no path exists
     */
00108     public double getPathLength(  ) {
        return m_pathLength;
    }


    /**
     * Convenience method to find the shortest path via a single static method
     * call.  If you need a more advanced search (e.g. limited by radius, or
     * computation of the path length), use the constructor instead.
     *
     * @param graph the graph to be searched
     * @param startVertex the vertex at which the path should start
     * @param endVertex the vertex at which the path should end
     *
     * @return List of Edges, or null if no path exists
     */
00124     public static List findPathBetween( Graph graph, Object startVertex,
        Object endVertex ) {
        DijkstraShortestPath alg =
            new DijkstraShortestPath( graph, startVertex, endVertex,
                Double.POSITIVE_INFINITY );

        return alg.getPathEdgeList(  );
    }


    private void createEdgeList( ClosestFirstIterator iter, Object endVertex ) {
        m_edgeList = new ArrayList(  );

        while( true ) {
            Edge edge = iter.getSpanningTreeEdge( endVertex );

            if( edge == null ) {
                break;
            }

            m_edgeList.add( edge );
            endVertex = edge.oppositeVertex( endVertex );
        }

        Collections.reverse( m_edgeList );
    }
}

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