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| package org.rblasch.convert.dijkstra; |
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| import org.rblasch.convert.graph.Connection; |
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| import org.rblasch.convert.graph.Edge; |
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| import org.rblasch.convert.graph.ListPath; |
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| import org.rblasch.convert.graph.Path; |
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| import org.rblasch.convert.graph.Vertex; |
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| import org.rblasch.convert.graph.WeightedDirectedGraph; |
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| import org.rblasch.convert.graph.WeightedEdge; |
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| import java.util.Collections; |
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| import java.util.Comparator; |
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| import java.util.HashMap; |
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| import java.util.HashSet; |
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| import java.util.Iterator; |
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| import java.util.LinkedList; |
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| import java.util.List; |
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| import java.util.Map; |
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| import java.util.Set; |
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| public class ShortestPathEngine { |
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| public static final int INFINITE_DISTANCE = Integer.MAX_VALUE; |
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| private final Comparator shortestDistanceComparator = new Comparator() { |
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| public int compare(final Object left, final Object right) {
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| return getShortestDistance((Vertex) left) - getShortestDistance((Vertex) right);
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| } |
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| }; |
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| private final WeightedDirectedGraph graph; |
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| private final Set unsettledNodes = new HashSet(); |
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| private final Set settledNodes = new HashSet(); |
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| private final Map shortestDistances = new HashMap(); |
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| private final Map predecessors = new HashMap(); |
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| public ShortestPathEngine(final WeightedDirectedGraph map) {
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| this.graph = map;
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| } |
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| private void init(final Vertex start) {
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| settledNodes.clear();
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| unsettledNodes.clear();
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| shortestDistances.clear();
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| predecessors.clear();
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| setShortestDistance(start, 0);
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| unsettledNodes.add(start);
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| } |
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| public void execute(final Vertex start, final Vertex destination) {
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| init(start);
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| Vertex u;
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| while ((u = extractMin()) != null) {
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| if (u == destination) break;
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| markSettled(u);
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| relaxNeighbors(u);
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| } |
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| } |
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| public Path getShortestPath(final Vertex start, final Vertex end) {
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| execute(start, end);
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| final List path = new LinkedList();
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| if (getShortestDistance(end) == ShortestPathEngine.INFINITE_DISTANCE) {
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| return null;
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| } |
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| Vertex nextVertex = end;
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| path.add(nextVertex);
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| while (nextVertex != null) {
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| final Vertex vertex = getPredecessor(nextVertex);
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| if (vertex != null) {
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| path.add(getMinWeightEdge(vertex, nextVertex));
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| path.add(vertex);
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| } |
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| nextVertex = vertex;
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| } |
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| Collections.reverse(path);
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| return new ListPath(path);
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| } |
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| private Edge getMinWeightEdge(final Vertex start, final Vertex end) {
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| return ((WeightedEdge) ((Connection) Collections.min(graph.getConnections(start, end), new Comparator() {
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| public int compare(final Object o1, final Object o2) {
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| final Connection c1 = (Connection) o1;
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| final Connection c2 = (Connection) o2;
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| return new Integer(((WeightedEdge) c1.getEdge()).getWeight()).compareTo(new Integer(((WeightedEdge) c2.getEdge()).getWeight()));
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| } |
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| })).getEdge()); |
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| } |
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| public int getMinWeight(final Vertex start, final Vertex end) {
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| return ((WeightedEdge) getMinWeightEdge(start, end)).getWeight();
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| } |
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| private Vertex extractMin() {
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| if (unsettledNodes.isEmpty()) return null;
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| final Object min = Collections.min(unsettledNodes, shortestDistanceComparator);
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| unsettledNodes.remove(min);
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| return (Vertex) min;
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| } |
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| private void relaxNeighbors(final Vertex u) {
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| for (Iterator i = graph.getOutbound(u).iterator(); i.hasNext();) {
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| final Vertex v = (Vertex) i.next();
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| if (isSettled(v)) continue;
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| if (getShortestDistance(v) > getShortestDistance(u) + getMinWeight(u, v)) {
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| setShortestDistance(v, getShortestDistance(u) + getMinWeight(u, v));
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| setPredecessor(v, u);
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| } |
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| } |
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| } |
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| private void markSettled(final Vertex u) {
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| settledNodes.add(u);
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| } |
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| private boolean isSettled(final Vertex v) {
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| return settledNodes.contains(v);
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| } |
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| public int getShortestDistance(final Vertex vertex) {
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| final Number d = (Number) shortestDistances.get(vertex);
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| return (d == null) ? INFINITE_DISTANCE : d.intValue();
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| } |
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| private void setShortestDistance(final Vertex vertex, final int distance) {
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| unsettledNodes.remove(vertex);
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| shortestDistances.put(vertex, new Integer(distance));
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| unsettledNodes.add(vertex);
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| } |
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| public Vertex getPredecessor(final Vertex vertex) {
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| return (Vertex) predecessors.get(vertex);
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| } |
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| private void setPredecessor(final Vertex a, final Vertex b) {
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| predecessors.put(a, b);
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| } |
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| } |