| /* |
| * Copyright 2014-present Open Networking Laboratory |
| * |
| * Licensed 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 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 |
| protected Result<V, E> internalSearch(Graph<V, E> graph, V src, V dst, |
| EdgeWeigher<V, E> weigher, int maxPaths) { |
| |
| // Use the default result to remember cumulative costs and parent |
| // edges to each each respective vertex. |
| DefaultResult result = new DefaultResult(src, dst, maxPaths); |
| |
| // Cost to reach the source vertex is 0 of course. |
| result.updateVertex(src, null, weigher.getInitialWeight(), false); |
| |
| if (graph.getEdges().isEmpty()) { |
| result.buildPaths(); |
| return result; |
| } |
| |
| // 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. |
| if (result.hasCost(nearest)) { |
| Weight cost = result.cost(nearest); |
| |
| // If the vertex is reachable, relax all its egress edges. |
| for (E e : graph.getEdgesFrom(nearest)) { |
| result.relaxEdge(e, cost, weigher, true); |
| } |
| } |
| |
| // 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) { |
| //not accessed vertices should be pushed to the back of the queue |
| if (!result.hasCost(v1) && !result.hasCost(v2)) { |
| return 0; |
| } else if (!result.hasCost(v1)) { |
| return -1; |
| } else if (!result.hasCost(v2)) { |
| return 1; |
| } |
| |
| return result.cost(v2).compareTo(result.cost(v1)); |
| } |
| } |
| |
| // 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); |
| } |
| |
| } |