| package org.onlab.graph; |
| |
| import java.util.ArrayList; |
| import java.util.Comparator; |
| import java.util.Set; |
| |
| /** |
| * Dijkstra shortest-path graph search algorithm capable of finding not just |
| * one, but all shortest paths between the source and destinations. |
| */ |
| public class DijkstraGraphSearch<V extends Vertex, E extends Edge<V>> |
| extends AbstractGraphPathSearch<V, E> { |
| |
| @Override |
| public Result<V, E> search(Graph<V, E> graph, V src, V dst, |
| EdgeWeight<V, E> weight) { |
| checkArguments(graph, src, dst); |
| |
| // Use the default result to remember cumulative costs and parent |
| // edges to each each respective vertex. |
| DefaultResult result = new DefaultResult(src, dst); |
| |
| // Cost to reach the source vertex is 0 of course. |
| result.updateVertex(src, null, 0.0, false); |
| |
| // Use the min priority queue to progressively find each nearest |
| // vertex until we reach the desired destination, if one was given, |
| // or until we reach all possible destinations. |
| Heap<V> minQueue = createMinQueue(graph.getVertexes(), |
| new PathCostComparator(result)); |
| while (!minQueue.isEmpty()) { |
| // Get the nearest vertex |
| V nearest = minQueue.extractExtreme(); |
| if (nearest.equals(dst)) { |
| break; |
| } |
| |
| // Find its cost and use it to determine if the vertex is reachable. |
| double cost = result.cost(nearest); |
| if (cost < Double.MAX_VALUE) { |
| // If the vertex is reachable, relax all its egress edges. |
| for (E e : graph.getEdgesFrom(nearest)) { |
| result.relaxEdge(e, cost, weight); |
| } |
| } |
| |
| // Re-prioritize the min queue. |
| minQueue.heapify(); |
| } |
| |
| // Now construct a set of paths from the results. |
| result.buildPaths(); |
| return result; |
| } |
| |
| // Compares path weights using their accrued costs; used for sorting the |
| // min priority queue. |
| private final class PathCostComparator implements Comparator<V> { |
| private final DefaultResult result; |
| |
| private PathCostComparator(DefaultResult result) { |
| this.result = result; |
| } |
| |
| @Override |
| public int compare(V v1, V v2) { |
| double delta = result.cost(v2) - result.cost(v1); |
| return delta < 0 ? -1 : (delta > 0 ? 1 : 0); |
| } |
| } |
| |
| // Creates a min priority queue from the specified vertexes and comparator. |
| private Heap<V> createMinQueue(Set<V> vertexes, Comparator<V> comparator) { |
| return new Heap<>(new ArrayList<>(vertexes), comparator); |
| } |
| |
| } |