| /* |
| * Copyright 2017-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 static com.google.common.base.Preconditions.checkNotNull; |
| import static java.util.Spliterators.spliteratorUnknownSize; |
| |
| import java.util.ArrayList; |
| import java.util.Comparator; |
| import java.util.Iterator; |
| import java.util.List; |
| import java.util.NoSuchElementException; |
| import java.util.PriorityQueue; |
| import java.util.Queue; |
| import java.util.Set; |
| import java.util.Spliterator; |
| import java.util.function.Supplier; |
| import java.util.stream.Stream; |
| import java.util.stream.StreamSupport; |
| |
| import com.google.common.base.Suppliers; |
| import com.google.common.collect.ComparisonChain; |
| import com.google.common.collect.ImmutableList; |
| import com.google.common.collect.Sets; |
| |
| /** |
| * Lazily runs K shortest paths algorithm on a provided directed graph. |
| */ |
| public class LazyKShortestPathsSearch<V extends Vertex, E extends Edge<V>> { |
| |
| private final Comparator<Path<V, E>> pathComparator = new PathComparator(); |
| |
| private final GraphPathSearch<V, E> shortest = new DijkstraGraphSearch<>(); |
| |
| /** |
| * Searches the specified graph for paths between vertices. |
| * |
| * @param graph graph to be searched |
| * @param src source vertex |
| * @param dst destination vertex |
| * @param weigher edge-weigher |
| * @return Stream of shortest paths |
| */ |
| public Stream<Path<V, E>> lazyPathSearch(Graph<V, E> graph, |
| V src, V dst, |
| EdgeWeigher<V, E> weigher) { |
| |
| Iterator<Path<V, E>> it = new ShortestPathIterator(graph, src, dst, weigher); |
| |
| return StreamSupport.stream(spliteratorUnknownSize(it, |
| Spliterator.ORDERED | |
| Spliterator.DISTINCT | |
| Spliterator.NONNULL | |
| Spliterator.IMMUTABLE), |
| false); |
| } |
| |
| /** |
| * Iterator returning shortest paths, searched incrementally on each next() call. |
| */ |
| private final class ShortestPathIterator implements Iterator<Path<V, E>> { |
| |
| final Graph<V, E> graph; |
| final V src; |
| final V dst; |
| final EdgeWeigher<V, E> weigher; |
| |
| final InnerEdgeWeigher maskingWeigher; |
| |
| final List<Path<V, E>> resultPaths = new ArrayList<>(); // A |
| final Queue<Path<V, E>> potentialPaths = new PriorityQueue<>(pathComparator); // B |
| |
| Supplier<Path<V, E>> next; |
| |
| ShortestPathIterator(Graph<V, E> graph, |
| V src, V dst, |
| EdgeWeigher<V, E> weigher) { |
| this.graph = checkNotNull(graph); |
| this.src = checkNotNull(src); |
| this.dst = checkNotNull(dst); |
| this.weigher = checkNotNull(weigher); |
| |
| maskingWeigher = new InnerEdgeWeigher(weigher); |
| next = Suppliers.ofInstance( |
| shortest.search(graph, src, dst, weigher, 1) |
| .paths().stream().findFirst().orElse(null)); |
| } |
| |
| @Override |
| public boolean hasNext() { |
| return next.get() != null; |
| } |
| |
| @Override |
| public Path<V, E> next() { |
| if (next.get() == null) { |
| throw new NoSuchElementException("No more path between " + src + "-" + dst); |
| } |
| |
| // lastPath: the path to return at the end of this call |
| Path<V, E> lastPath = next.get(); |
| resultPaths.add(lastPath); |
| |
| next = Suppliers.memoize(() -> computeNext(lastPath)); |
| |
| return lastPath; |
| } |
| |
| private Path<V, E> computeNext(Path<V, E> lastPath) { |
| /// following is basically Yen's k-shortest path algorithm |
| |
| // start searching for next path |
| for (int i = 0; i < lastPath.edges().size(); i++) { |
| V spurNode = lastPath.edges().get(i).src(); |
| List<E> rootPathEdgeList = lastPath.edges().subList(0, i); |
| |
| for (Path<V, E> path : resultPaths) { |
| if (path.edges().size() >= i && |
| rootPathEdgeList.equals(path.edges().subList(0, i))) { |
| maskingWeigher.excluded.add(path.edges().get(i)); |
| } |
| } |
| |
| // Effectively remove all root path nodes other than spurNode |
| rootPathEdgeList.forEach(edge -> { |
| maskingWeigher.excluded.addAll(graph.getEdgesFrom(edge.src())); |
| maskingWeigher.excluded.addAll(graph.getEdgesTo(edge.src())); |
| }); |
| |
| shortest.search(graph, spurNode, dst, maskingWeigher, 1) |
| .paths().stream().findAny().ifPresent(spurPath -> { |
| |
| List<E> totalPath = ImmutableList.<E>builder() |
| .addAll(rootPathEdgeList) |
| .addAll(spurPath.edges()) |
| .build(); |
| potentialPaths.add(path(totalPath)); |
| }); |
| |
| // Restore all removed paths and nodes |
| maskingWeigher.excluded.clear(); |
| } |
| |
| if (potentialPaths.isEmpty()) { |
| return null; |
| } else { |
| return potentialPaths.poll(); |
| } |
| } |
| |
| private Path<V, E> path(List<E> edges) { |
| //The following line must use the original weigher not the modified weigher because the modified |
| //weigher will count -1 values used for modifying the graph and return an inaccurate cost. |
| return new DefaultPath<>(edges, calculatePathCost(weigher, edges)); |
| } |
| |
| private Weight calculatePathCost(EdgeWeigher<V, E> weighter, List<E> edges) { |
| Weight totalCost = weighter.getInitialWeight(); |
| for (E edge : edges) { |
| totalCost = totalCost.merge(weighter.weight(edge)); |
| } |
| return totalCost; |
| } |
| } |
| |
| /** |
| * EdgeWeigher which excludes specified edges from path computation. |
| */ |
| private final class InnerEdgeWeigher implements EdgeWeigher<V, E> { |
| |
| private final Set<E> excluded = Sets.newConcurrentHashSet(); |
| private final EdgeWeigher<V, E> weigher; |
| |
| private InnerEdgeWeigher(EdgeWeigher<V, E> weigher) { |
| this.weigher = weigher; |
| } |
| |
| @Override |
| public Weight weight(E edge) { |
| if (excluded.contains(edge)) { |
| return weigher.getNonViableWeight(); |
| } |
| return weigher.weight(edge); |
| } |
| |
| @Override |
| public Weight getInitialWeight() { |
| return weigher.getInitialWeight(); |
| } |
| |
| @Override |
| public Weight getNonViableWeight() { |
| return weigher.getNonViableWeight(); |
| } |
| } |
| |
| /** |
| * Provides a comparator to order the set of paths. |
| * Compare by cost, then by hop count. |
| */ |
| private final class PathComparator implements Comparator<Path<V, E>> { |
| |
| @Override |
| public int compare(Path<V, E> pathOne, Path<V, E> pathTwo) { |
| return ComparisonChain.start() |
| .compare(pathOne.cost(), pathTwo.cost()) |
| .compare(pathOne.edges().size(), pathTwo.edges().size()) |
| .result(); |
| } |
| } |
| |
| } |