| /* |
| * Copyright 2015 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.Set; |
| import java.util.List; |
| import java.util.Map; |
| import java.util.HashMap; |
| import java.util.HashSet; |
| import java.util.stream.Collectors; |
| |
| /** |
| * Suurballe shortest-path graph search algorithm capable of finding both |
| * a shortest path, as well as a backup shortest path, between a source and a destination |
| * such that the sum of the path lengths is minimized. |
| */ |
| public class SuurballeGraphSearch<V extends Vertex, E extends Edge<V>> extends DijkstraGraphSearch<V, E> { |
| |
| @Override |
| public Result<V, E> search(Graph<V, E> graph, V src, V dst, |
| EdgeWeight<V, E> weight, int maxPaths) { |
| |
| if (weight == null) { |
| weight = edge -> 1; |
| } |
| |
| List<DisjointPathPair<V, E>> dpps = new ArrayList<>(); |
| |
| final EdgeWeight weightf = weight; |
| DefaultResult firstDijkstraS = (DefaultResult) super.search(graph, src, dst, weight, ALL_PATHS); |
| DefaultResult firstDijkstra = (DefaultResult) super.search(graph, src, null, weight, ALL_PATHS); |
| |
| //choose an arbitrary shortest path to run Suurballe on |
| Path<V, E> shortPath = null; |
| if (firstDijkstraS.paths().size() == 0) { |
| return firstDijkstraS; |
| } |
| for (Path p: firstDijkstraS.paths()) { |
| shortPath = p; |
| //transforms the graph so tree edges have 0 weight |
| EdgeWeight<V, Edge<V>> modified = edge -> { |
| if (classE().isInstance(edge)) { |
| return weightf.weight((E) (edge)) + firstDijkstra.cost(edge.src()) |
| - firstDijkstra.cost(edge.dst()); |
| } |
| return 0; |
| }; |
| EdgeWeight<V, E> modified2 = edge -> |
| weightf.weight(edge) + firstDijkstra.cost(edge.src()) - firstDijkstra.cost(edge.dst()); |
| |
| //create a residual graph g' by removing all src vertices and reversing 0 length path edges |
| MutableGraph<V, Edge<V>> gt = mutableCopy(graph); |
| |
| Map<Edge<V>, E> revToEdge = new HashMap<>(); |
| graph.getEdgesTo(src).forEach(gt::removeEdge); |
| for (E edge: shortPath.edges()) { |
| gt.removeEdge(edge); |
| Edge<V> reverse = new Edge<V>() { |
| final Edge<V> orig = edge; |
| public V src() { |
| return orig.dst(); |
| } |
| public V dst() { |
| return orig.src(); |
| } |
| public String toString() { |
| return "ReversedEdge " + "src=" + src() + " dst=" + dst(); |
| } |
| }; |
| revToEdge.put(reverse, edge); |
| gt.addEdge(reverse); |
| } |
| |
| //rerun dijkstra on the temporary graph to get a second path |
| Result<V, Edge<V>> secondDijkstra; |
| secondDijkstra = new DijkstraGraphSearch<V, Edge<V>>().search(gt, src, dst, modified, ALL_PATHS); |
| |
| Path<V, Edge<V>> residualShortPath = null; |
| if (secondDijkstra.paths().size() == 0) { |
| dpps.add(new DisjointPathPair<V, E>(shortPath, null)); |
| continue; |
| } |
| |
| for (Path p2: secondDijkstra.paths()) { |
| residualShortPath = p2; |
| |
| MutableGraph<V, E> roundTrip = mutableCopy(graph); |
| |
| List<E> tmp = roundTrip.getEdges().stream().collect(Collectors.toList()); |
| |
| tmp.forEach(roundTrip::removeEdge); |
| |
| shortPath.edges().forEach(roundTrip::addEdge); |
| |
| if (residualShortPath != null) { |
| for (Edge<V> edge: residualShortPath.edges()) { |
| if (classE().isInstance(edge)) { |
| roundTrip.addEdge((E) edge); |
| } else { |
| roundTrip.removeEdge(revToEdge.get(edge)); |
| } |
| } |
| } |
| //Actually build the final result |
| DefaultResult lastSearch = (DefaultResult) super.search(roundTrip, src, dst, weight, ALL_PATHS); |
| Path<V, E> path1 = lastSearch.paths().iterator().next(); |
| path1.edges().forEach(roundTrip::removeEdge); |
| |
| Set<Path<V, E>> bckpaths = super.search(roundTrip, src, dst, weight, ALL_PATHS).paths(); |
| Path<V, E> backup = null; |
| if (bckpaths.size() != 0) { |
| backup = bckpaths.iterator().next(); |
| } |
| |
| dpps.add(new DisjointPathPair<>(path1, backup)); |
| } |
| } |
| |
| for (int i = dpps.size() - 1; i > 0; i--) { |
| if (dpps.get(i).size() <= 1) { |
| dpps.remove(i); |
| } |
| } |
| |
| return new Result<V, E>() { |
| final DefaultResult search = firstDijkstra; |
| |
| public V src() { |
| return src; |
| } |
| public V dst() { |
| return dst; |
| } |
| public Set<Path<V, E>> paths() { |
| Set<Path<V, E>> pathsD = new HashSet<>(); |
| int paths = 0; |
| for (DisjointPathPair<V, E> path: dpps) { |
| pathsD.add((Path<V, E>) path); |
| paths++; |
| if (paths == maxPaths) { |
| break; |
| } |
| } |
| return pathsD; |
| } |
| public Map<V, Double> costs() { |
| return search.costs(); |
| } |
| public Map<V, Set<E>> parents() { |
| return search.parents(); |
| } |
| }; |
| } |
| |
| private Class<?> clazzV; |
| |
| public Class<?> classV() { |
| return clazzV; |
| } |
| |
| private Class<?> clazzE; |
| |
| public Class<?> classE() { |
| return clazzE; |
| } |
| /** |
| * Creates a mutable copy of an immutable graph. |
| * |
| * @param graph immutable graph |
| * @return mutable copy |
| */ |
| public MutableGraph mutableCopy(Graph<V, E> graph) { |
| clazzV = graph.getVertexes().iterator().next().getClass(); |
| clazzE = graph.getEdges().iterator().next().getClass(); |
| return new MutableAdjacencyListsGraph<V, E>(graph.getVertexes(), graph.getEdges()); |
| } |
| } |
| |