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DijkstraWhichToOne.java
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DijkstraWhichToOne.java
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/*
* Licensed to GraphHopper and Peter Karich under one or more contributor
* license agreements. See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*
* GraphHopper licenses this file to you under the Apache License,
* Version 2.0 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.graphhopper.routing.rideshare;
import com.graphhopper.routing.AbstractRoutingAlgorithm;
import com.graphhopper.routing.Path;
import com.graphhopper.routing.PathBidirRef;
import com.graphhopper.routing.util.EdgeFilter;
import com.graphhopper.routing.util.FlagEncoder;
import com.graphhopper.routing.util.WeightCalculation;
import com.graphhopper.storage.EdgeEntry;
import com.graphhopper.storage.Graph;
import com.graphhopper.util.EdgeExplorer;
import com.graphhopper.util.EdgeIterator;
import gnu.trove.list.array.TIntArrayList;
import gnu.trove.map.TIntObjectMap;
import gnu.trove.map.hash.TIntObjectHashMap;
import java.util.PriorityQueue;
/**
* Public transport represents a collection of Locations. Now it is the aim to find the shortest
* path of a path ('the public transport') to the destination. In contrast to manyToOne this class
* only find one shortest path and not all, but it it more memory efficient (ie. the
* shortest-path-trees do not overlap here)
* <p/>
* @author Peter Karich
*/
public class DijkstraWhichToOne extends AbstractRoutingAlgorithm
{
private PathBidirRef shortest;
private TIntObjectMap<EdgeEntry> shortestDistMapOther;
private TIntObjectMap<EdgeEntry> shortestDistMapFrom;
private TIntObjectMap<EdgeEntry> shortestDistMapTo;
private TIntArrayList pubTransport = new TIntArrayList();
private int destination;
private int visitedFromCount;
private int visitedToCount;
public DijkstraWhichToOne( Graph graph, FlagEncoder encoder, WeightCalculation type )
{
super(graph, encoder, type);
}
public void addPubTransportPoints( int... indices )
{
if (indices.length == 0)
{
throw new IllegalStateException("You need to add something");
}
for (int i = 0; i < indices.length; i++)
{
addPubTransportPoint(indices[i]);
}
}
public void addPubTransportPoint( int index )
{
if (!pubTransport.contains(index))
{
pubTransport.add(index);
}
}
public void setDestination( int index )
{
destination = index;
}
public Path calcPath()
{
// identical
if (pubTransport.contains(destination))
{
return new Path(graph, flagEncoder);
}
PriorityQueue<EdgeEntry> prioQueueFrom = new PriorityQueue<EdgeEntry>();
shortestDistMapFrom = new TIntObjectHashMap<EdgeEntry>();
EdgeEntry entryTo = new EdgeEntry(EdgeIterator.NO_EDGE, destination, 0);
EdgeEntry currTo = entryTo;
PriorityQueue<EdgeEntry> prioQueueTo = new PriorityQueue<EdgeEntry>();
shortestDistMapTo = new TIntObjectHashMap<EdgeEntry>();
shortestDistMapTo.put(destination, entryTo);
shortest = new PathBidirRef(graph, flagEncoder);
// create several starting points
if (pubTransport.isEmpty())
{
throw new IllegalStateException("You'll need at least one starting point. Set it via addPubTransportPoint");
}
EdgeEntry currFrom = null;
for (int i = 0; i < pubTransport.size(); i++)
{
EdgeEntry tmpFrom = new EdgeEntry(EdgeIterator.NO_EDGE, pubTransport.get(i), 0);
if (i == 0)
{
currFrom = tmpFrom;
}
shortestDistMapOther = shortestDistMapTo;
fillEdges(shortest, tmpFrom, prioQueueFrom, shortestDistMapFrom, outEdgeExplorer);
}
int finish = 0;
while (finish < 2 && currFrom.weight + currTo.weight < shortest.getWeight())
{
// http://www.cs.princeton.edu/courses/archive/spr06/cos423/Handouts/EPP%20shortest%20path%20algorithms.pdf
// a node from overlap may not be on the shortest path!!
// => when scanning an arc (v, w) in the forward search and w is scanned in the reverse
// search, update shortest = μ if df (v) + (v, w) + dr (w) < μ
finish = 0;
shortestDistMapOther = shortestDistMapTo;
fillEdges(shortest, currFrom, prioQueueFrom, shortestDistMapFrom, outEdgeExplorer);
if (!prioQueueFrom.isEmpty())
{
currFrom = prioQueueFrom.poll();
} else
{
finish++;
}
shortestDistMapOther = shortestDistMapFrom;
fillEdges(shortest, currTo, prioQueueTo, shortestDistMapTo, inEdgeExplorer);
if (!prioQueueTo.isEmpty())
{
currTo = prioQueueTo.poll();
} else
{
finish++;
}
}
Path p = shortest.extract();
if (!p.isFound())
{
return p;
}
return p;
}
void fillEdges( PathBidirRef shortest, EdgeEntry curr,
PriorityQueue<EdgeEntry> prioQueue,
TIntObjectMap<EdgeEntry> shortestDistMap, EdgeExplorer explorer )
{
int currNode = curr.endNode;
EdgeIterator iter = explorer.setBaseNode(currNode);
while (iter.next())
{
int tmpV = iter.getAdjNode();
double tmp = weightCalc.getWeight(iter.getDistance(), iter.getFlags()) + curr.weight;
EdgeEntry de = shortestDistMap.get(tmpV);
if (de == null)
{
de = new EdgeEntry(iter.getEdge(), tmpV, tmp);
de.parent = curr;
shortestDistMap.put(tmpV, de);
prioQueue.add(de);
} else if (de.weight > tmp)
{
prioQueue.remove(de);
de.edge = iter.getEdge();
de.weight = tmp;
de.parent = curr;
prioQueue.add(de);
}
updateShortest(de, tmpV);
}
}
@Override
public void updateShortest( EdgeEntry de, int currLoc )
{
EdgeEntry entryOther = shortestDistMapOther.get(currLoc);
if (entryOther != null)
{
// update μ
double newShortest = de.weight + entryOther.weight;
if (newShortest < shortest.getWeight())
{
shortest.setSwitchToFrom(shortestDistMapFrom == shortestDistMapOther);
shortest.setEdgeEntry(de);
shortest.setEdgeEntryTo(entryOther);
shortest.setWeight(newShortest);
}
}
}
@Override
public Path calcPath( int from, int to )
{
addPubTransportPoint(from);
setDestination(to);
return calcPath();
}
@Override
public int getVisitedNodes()
{
return visitedFromCount + visitedToCount;
}
}