DijkstraShortestPath

/*
* Copyright (c) 2003, The JUNG Authors
*
* All rights reserved.
*
* This software is open-source under the BSD license; see either
* "license.txt" or
* https://github.com/jrtom/jung/blob/master/LICENSE for a description.
*/
package edu.uci.ics.jung.algorithms.shortestpath;

import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

import com.google.common.base.Function;

import edu.uci.ics.jung.graph.Graph;

/**
 * <p>Calculates distances and shortest paths using Dijkstra's
 * single-source-shortest-path algorithm.  This is a lightweight
 * extension of <code>DijkstraDistance</code> that also stores
 * path information, so that the shortest paths can be reconstructed.
 *
 * <p> The elements in the maps returned by
 * <code>getIncomingEdgeMap</code> are ordered (that is, returned
 * by the iterator) by nondecreasing distance from <code>source</code>.
 *
 * @author Joshua O'Madadhain
 * @author Tom Nelson converted to jung2
 * @see DijkstraDistance
 */
public class DijkstraShortestPath<V,E> extends DijkstraDistance<V,E> implements ShortestPath<V,E>
{
    /**
     * <p>Creates an instance of <code>DijkstraShortestPath</code> for
     * the specified graph and the specified method of extracting weights
     * from edges, which caches results locally if and only if
     * <code>cached</code> is <code>true</code>.
     *
     * @param g     the graph on which distances will be calculated
     * @param nev   the class responsible for returning weights for edges
     * @param cached    specifies whether the results are to be cached
     */
    public DijkstraShortestPath(Graph<V,E> g, Function<E, ? extends Number> nev, boolean cached)
    {
        super(g, nev, cached);
    }

    /**
     * <p>Creates an instance of <code>DijkstraShortestPath</code> for
     * the specified graph and the specified method of extracting weights
     * from edges, which caches results locally.
     *
     * @param g     the graph on which distances will be calculated
     * @param nev   the class responsible for returning weights for edges
     */
    public DijkstraShortestPath(Graph<V,E> g, Function<E, ? extends Number> nev)
    {
        super(g, nev);
    }

    /**
     * <p>Creates an instance of <code>DijkstraShortestPath</code> for
     * the specified unweighted graph (that is, all weights 1) which
     * caches results locally.
     *
     * @param g     the graph on which distances will be calculated
     */
    public DijkstraShortestPath(Graph<V,E> g)
    {
        super(g);
    }

    /**
     * <p>Creates an instance of <code>DijkstraShortestPath</code> for
     * the specified unweighted graph (that is, all weights 1) which
     * caches results locally.
     *
     * @param g     the graph on which distances will be calculated
     * @param cached    specifies whether the results are to be cached
     */
    public DijkstraShortestPath(Graph<V,E> g, boolean cached)
    {
        super(g, cached);
    }

    @Override
    protected SourceData getSourceData(V source)
    {
        SourceData sd = sourceMap.get(source);
        if (sd == null)
            sd = new SourcePathData(source);
        return sd;
    }

    /**
     * <p>Returns the last edge on a shortest path from <code>source</code>
     * to <code>target</code>, or null if <code>target</code> is not
     * reachable from <code>source</code>.
     *
     * <p>If either vertex is not in the graph for which this instance
     * was created, throws <code>IllegalArgumentException</code>.
     *
     * @param source the vertex where the shortest path starts
     * @param target the vertex where the shortest path ends
     * @return the last edge on a shortest path from {@code source} to {@code target}
     *     or null if {@code target} is not reachable from {@code source}
     */
	public E getIncomingEdge(V source, V target)
	{
        if (!g.containsVertex(source))
            throw new IllegalArgumentException("Specified source vertex " +
                    source + " is not part of graph " + g);

        if (!g.containsVertex(target))
            throw new IllegalArgumentException("Specified target vertex " +
                    target + " is not part of graph " + g);

        Set<V> targets = new HashSet<V>();
        targets.add(target);
        singleSourceShortestPath(source, targets, g.getVertexCount());
        @SuppressWarnings("unchecked")
		Map<V,E> incomingEdgeMap =
            ((SourcePathData)sourceMap.get(source)).incomingEdges;
        E incomingEdge = incomingEdgeMap.get(target);

        if (!cached)
            reset(source);

        return incomingEdge;
	}

    /**
     * <p>Returns a <code>LinkedHashMap</code> which maps each vertex
     * in the graph (including the <code>source</code> vertex)
     * to the last edge on the shortest path from the
     * <code>source</code> vertex.
     * The map's iterator will return the elements in order of
     * increasing distance from <code>source</code>.
     *
     * @see DijkstraDistance#getDistanceMap(Object,int)
     * @see DijkstraDistance#getDistance(Object,Object)
     * @param source    the vertex from which distances are measured
     */
    public Map<V,E> getIncomingEdgeMap(V source)
	{
		return getIncomingEdgeMap(source, g.getVertexCount());
	}

    /**
     * Returns a <code>List</code> of the edges on the shortest path from
     * <code>source</code> to <code>target</code>, in order of their
     * occurrence on this path.
     * If either vertex is not in the graph for which this instance
     * was created, throws <code>IllegalArgumentException</code>.
     *
     * @param source the starting vertex for the path to generate
     * @param target the ending vertex for the path to generate
     * @return the edges on the shortest path from {@code source} to {@code target},
     *     in order of their occurrence
     */
	public List<E> getPath(V source, V target)
	{
		if(!g.containsVertex(source))
            throw new IllegalArgumentException("Specified source vertex " +
                    source + " is not part of graph " + g);

		if(!g.containsVertex(target))
            throw new IllegalArgumentException("Specified target vertex " +
                    target + " is not part of graph " + g);

        LinkedList<E> path = new LinkedList<E>();

        // collect path data; must use internal method rather than
        // calling getIncomingEdge() because getIncomingEdge() may
        // wipe out results if results are not cached
        Set<V> targets = new HashSet<V>();
        targets.add(target);
        singleSourceShortestPath(source, targets, g.getVertexCount());
        @SuppressWarnings("unchecked")
		Map<V,E> incomingEdges =
            ((SourcePathData)sourceMap.get(source)).incomingEdges;

        if (incomingEdges.isEmpty() || incomingEdges.get(target) == null)
            return path;
        V current = target;
        while (!current.equals(source))
        {
            E incoming = incomingEdges.get(current);
            path.addFirst(incoming);
            current = ((Graph<V,E>)g).getOpposite(current, incoming);
        }
		return path;
	}


    /**
     * <p>Returns a <code>LinkedHashMap</code> which maps each of the closest
     * <code>numDests</code> vertices to the <code>source</code> vertex
     * in the graph (including the <code>source</code> vertex)
     * to the incoming edge along the path from that vertex.  Throws
     * an <code>IllegalArgumentException</code> if <code>source</code>
     * is not in this instance's graph, or if <code>numDests</code> is
     * either less than 1 or greater than the number of vertices in the
     * graph.
     *
     * @see #getIncomingEdgeMap(Object)
     * @see #getPath(Object,Object)
     * @param source    the vertex from which distances are measured
     * @param numDests  the number of vertices for which to measure distances
     * @return a map from each of the closest {@code numDests} vertices
     *     to the last edge on the shortest path to that vertex starting from {@code source}
     */
	public LinkedHashMap<V,E> getIncomingEdgeMap(V source, int numDests)
	{
        if (g.getVertices().contains(source) == false)
            throw new IllegalArgumentException("Specified source vertex " +
                    source + " is not part of graph " + g);

        if (numDests < 1 || numDests > g.getVertexCount())
            throw new IllegalArgumentException("numDests must be >= 1 " +
            "and <= g.numVertices()");

        singleSourceShortestPath(source, null, numDests);

        @SuppressWarnings("unchecked")
		LinkedHashMap<V,E> incomingEdgeMap =
            ((SourcePathData)sourceMap.get(source)).incomingEdges;

        if (!cached)
            reset(source);

        return incomingEdgeMap;
	}


    /**
     * For a given source vertex, holds the estimated and final distances,
     * tentative and final assignments of incoming edges on the shortest path from
     * the source vertex, and a priority queue (ordered by estimaed distance)
     * of the vertices for which distances are unknown.
     *
     * @author Joshua O'Madadhain
     */
    protected class SourcePathData extends SourceData
    {
        protected Map<V,E> tentativeIncomingEdges;
		protected LinkedHashMap<V,E> incomingEdges;

		protected SourcePathData(V source)
		{
            super(source);
            incomingEdges = new LinkedHashMap<V,E>();
            tentativeIncomingEdges = new HashMap<V,E>();
		}

        @Override
        public void update(V dest, E tentative_edge, double new_dist)
        {
            super.update(dest, tentative_edge, new_dist);
            tentativeIncomingEdges.put(dest, tentative_edge);
        }

        @Override
        public Map.Entry<V,Number> getNextVertex()
        {
            Map.Entry<V,Number> p = super.getNextVertex();
            V v = p.getKey();
            E incoming = tentativeIncomingEdges.remove(v);
            incomingEdges.put(v, incoming);
            return p;
        }

        @Override
        public void restoreVertex(V v, double dist)
        {
            super.restoreVertex(v, dist);
            E incoming = incomingEdges.get(v);
            tentativeIncomingEdges.put(v, incoming);
        }

        @Override
        public void createRecord(V w, E e, double new_dist)
        {
            super.createRecord(w, e, new_dist);
            tentativeIncomingEdges.put(w, e);
        }

    }

}