| /* |
| * Copyright 2015-present Open Networking Foundation |
| * |
| * 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 com.google.common.collect.Sets; |
| |
| 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 |
| protected Result<V, E> internalSearch(Graph<V, E> graph, V src, V dst, |
| EdgeWeigher<V, E> weigher, int maxPaths) { |
| // FIXME: This method needs to be refactored as it is difficult to follow and debug. |
| |
| // FIXME: There is a defect here triggered by 3+ edges between the same vertices, |
| // which makes an attempt to produce looping paths. Protection against |
| // this was added to AbstractGraphPathSearch, but the root issue remains here. |
| |
| // FIXME: There is a defect here where not all paths are truly disjoint. |
| // This class needs to filter its own results to make sure that the |
| // paths are indeed disjoint. Temporary fix for this is provided, but |
| // the issue needs to be addressed through refactoring. |
| |
| EdgeWeigher weightf = weigher; |
| DefaultResult firstDijkstraS = (DefaultResult) super.internalSearch( |
| graph, src, dst, weigher, ALL_PATHS); |
| DefaultResult firstDijkstra = (DefaultResult) super.internalSearch( |
| graph, src, null, weigher, ALL_PATHS); |
| |
| //choose an arbitrary shortest path to run Suurballe on |
| Path<V, E> shortPath = null; |
| if (firstDijkstraS.paths().isEmpty()) { |
| return firstDijkstraS; |
| } |
| |
| DisjointPathResult result = new DisjointPathResult(firstDijkstra, src, dst, maxPaths); |
| |
| for (Path p: firstDijkstraS.paths()) { |
| shortPath = p; |
| //transforms the graph so tree edges have 0 weight |
| EdgeWeigher<V, E> modified = new EdgeWeigher<V, E>() { |
| @Override |
| public Weight weight(E edge) { |
| return edge instanceof ReverseEdge ? |
| weightf.getInitialWeight() : |
| weightf.weight(edge).merge(firstDijkstra.cost(edge.src())) |
| .subtract(firstDijkstra.cost(edge.dst())); |
| } |
| |
| @Override |
| public Weight getInitialWeight() { |
| return weightf.getInitialWeight(); |
| } |
| |
| @Override |
| public Weight getNonViableWeight() { |
| return weightf.getNonViableWeight(); |
| } |
| }; |
| |
| EdgeWeigher<V, E> modified2 = new EdgeWeigher<V, E>() { |
| @Override |
| public Weight weight(E edge) { |
| return weightf.weight(edge).merge(firstDijkstra.cost(edge.src())) |
| .subtract(firstDijkstra.cost(edge.dst())); |
| } |
| |
| @Override |
| public Weight getInitialWeight() { |
| return weightf.getInitialWeight(); |
| } |
| |
| @Override |
| public Weight getNonViableWeight() { |
| return weightf.getNonViableWeight(); |
| } |
| }; |
| |
| //create a residual graph g' by removing all src vertices and reversing 0 length path edges |
| MutableGraph<V, E> gt = mutableCopy(graph); |
| |
| Map<E, E> revToEdge = new HashMap<>(); |
| graph.getEdgesTo(src).forEach(gt::removeEdge); |
| for (E edge: shortPath.edges()) { |
| gt.removeEdge(edge); |
| Edge<V> reverse = new ReverseEdge<V>(edge); |
| revToEdge.put((E) reverse, edge); |
| gt.addEdge((E) reverse); |
| } |
| |
| //rerun dijkstra on the temporary graph to get a second path |
| Result<V, E> secondDijkstra = new DijkstraGraphSearch<V, E>() |
| .search(gt, src, dst, modified, ALL_PATHS); |
| |
| Path<V, E> residualShortPath = null; |
| if (secondDijkstra.paths().isEmpty()) { |
| result.dpps.add(new DisjointPathPair<>(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 (edge instanceof ReverseEdge) { |
| roundTrip.removeEdge(revToEdge.get(edge)); |
| } else { |
| roundTrip.addEdge((E) edge); |
| } |
| } |
| } |
| //Actually build the final result |
| DefaultResult lastSearch = (DefaultResult) |
| super.internalSearch(roundTrip, src, dst, weigher, ALL_PATHS); |
| Path<V, E> primary = lastSearch.paths().iterator().next(); |
| primary.edges().forEach(roundTrip::removeEdge); |
| |
| Set<Path<V, E>> backups = super.internalSearch(roundTrip, src, dst, |
| weigher, ALL_PATHS).paths(); |
| |
| // Find first backup path that does not share any nodes with the primary |
| for (Path<V, E> backup : backups) { |
| if (isDisjoint(primary, backup)) { |
| result.dpps.add(new DisjointPathPair<>(primary, backup)); |
| break; |
| } |
| } |
| } |
| } |
| |
| for (int i = result.dpps.size() - 1; i > 0; i--) { |
| if (result.dpps.get(i).size() <= 1) { |
| result.dpps.remove(i); |
| } |
| } |
| |
| result.buildPaths(); |
| return result; |
| } |
| |
| private boolean isDisjoint(Path<V, E> a, Path<V, E> b) { |
| return Sets.intersection(vertices(a), vertices(b)).isEmpty(); |
| } |
| |
| private Set<V> vertices(Path<V, E> p) { |
| Set<V> set = new HashSet<>(); |
| p.edges().forEach(e -> set.add(e.src())); |
| set.remove(p.src()); |
| return set; |
| } |
| |
| /** |
| * Creates a mutable copy of an immutable graph. |
| * |
| * @param graph immutable graph |
| * @return mutable copy |
| */ |
| private MutableGraph<V, E> mutableCopy(Graph<V, E> graph) { |
| return new MutableAdjacencyListsGraph<>(graph.getVertexes(), graph.getEdges()); |
| } |
| |
| private static final class ReverseEdge<V extends Vertex> extends AbstractEdge<V> { |
| private ReverseEdge(Edge<V> edge) { |
| super(edge.dst(), edge.src()); |
| } |
| |
| @Override |
| public String toString() { |
| return "ReversedEdge " + "src=" + src() + " dst=" + dst(); |
| } |
| } |
| |
| // Auxiliary result for disjoint path search |
| private final class DisjointPathResult implements AbstractGraphPathSearch.Result<V, E> { |
| |
| private final Result<V, E> searchResult; |
| private final V src, dst; |
| private final int maxPaths; |
| private final List<DisjointPathPair<V, E>> dpps = new ArrayList<>(); |
| private final Set<Path<V, E>> disjointPaths = new HashSet<>(); |
| |
| private DisjointPathResult(Result<V, E> searchResult, V src, V dst, int maxPaths) { |
| this.searchResult = searchResult; |
| this.src = src; |
| this.dst = dst; |
| this.maxPaths = maxPaths; |
| } |
| |
| @Override |
| public V src() { |
| return src; |
| } |
| |
| @Override |
| public V dst() { |
| return dst; |
| } |
| |
| @Override |
| public Set<Path<V, E>> paths() { |
| return disjointPaths; |
| } |
| |
| private void buildPaths() { |
| int paths = 0; |
| for (DisjointPathPair<V, E> path: dpps) { |
| disjointPaths.add(path); |
| paths++; |
| if (paths == maxPaths) { |
| break; |
| } |
| } |
| } |
| |
| @Override |
| public Map<V, Set<E>> parents() { |
| return searchResult.parents(); |
| } |
| |
| @Override |
| public Map<V, Weight> costs() { |
| return searchResult.costs(); |
| } |
| } |
| } |
| |