Yuta HIGUCHI | e3ebe69 | 2017-04-17 10:00:42 -0700 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2017-present Open Networking Laboratory |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | package org.onlab.graph; |
| 17 | |
| 18 | import static com.google.common.base.Preconditions.checkNotNull; |
| 19 | import static java.util.Spliterators.spliteratorUnknownSize; |
| 20 | |
| 21 | import java.util.ArrayList; |
| 22 | import java.util.Comparator; |
| 23 | import java.util.Iterator; |
| 24 | import java.util.List; |
| 25 | import java.util.NoSuchElementException; |
| 26 | import java.util.PriorityQueue; |
| 27 | import java.util.Queue; |
| 28 | import java.util.Set; |
| 29 | import java.util.Spliterator; |
| 30 | import java.util.stream.Stream; |
| 31 | import java.util.stream.StreamSupport; |
| 32 | |
| 33 | import com.google.common.collect.ComparisonChain; |
| 34 | import com.google.common.collect.ImmutableList; |
| 35 | import com.google.common.collect.Sets; |
| 36 | |
| 37 | /** |
| 38 | * Lazily runs K shortest paths algorithm on a provided directed graph. |
| 39 | */ |
| 40 | public class LazyKShortestPathsSearch<V extends Vertex, E extends Edge<V>> { |
| 41 | |
| 42 | private final Comparator<Path<V, E>> pathComparator = new PathComparator(); |
| 43 | |
| 44 | private final GraphPathSearch<V, E> shortest = new DijkstraGraphSearch<>(); |
| 45 | |
| 46 | /** |
| 47 | * Searches the specified graph for paths between vertices. |
| 48 | * |
| 49 | * @param graph graph to be searched |
| 50 | * @param src source vertex |
| 51 | * @param dst destination vertex |
| 52 | * @param weigher edge-weigher |
| 53 | * @return Stream of shortest paths |
| 54 | */ |
| 55 | public Stream<Path<V, E>> lazyPathSearch(Graph<V, E> graph, |
| 56 | V src, V dst, |
| 57 | EdgeWeigher<V, E> weigher) { |
| 58 | |
| 59 | Iterator<Path<V, E>> it = new ShortestPathIterator(graph, src, dst, weigher); |
| 60 | |
| 61 | return StreamSupport.stream(spliteratorUnknownSize(it, |
| 62 | Spliterator.ORDERED | |
| 63 | Spliterator.DISTINCT | |
| 64 | Spliterator.NONNULL | |
| 65 | Spliterator.IMMUTABLE), |
| 66 | false); |
| 67 | } |
| 68 | |
| 69 | /** |
| 70 | * Iterator returning shortest paths, searched incrementally on each next() call. |
| 71 | */ |
| 72 | private final class ShortestPathIterator implements Iterator<Path<V, E>> { |
| 73 | |
| 74 | final Graph<V, E> graph; |
| 75 | final V src; |
| 76 | final V dst; |
| 77 | final EdgeWeigher<V, E> weigher; |
| 78 | |
| 79 | final InnerEdgeWeigher maskingWeigher; |
| 80 | |
| 81 | final List<Path<V, E>> resultPaths = new ArrayList<>(); // A |
| 82 | final Queue<Path<V, E>> potentialPaths = new PriorityQueue<>(pathComparator); // B |
| 83 | |
| 84 | Path<V, E> next; |
| 85 | |
| 86 | ShortestPathIterator(Graph<V, E> graph, |
| 87 | V src, V dst, |
| 88 | EdgeWeigher<V, E> weigher) { |
| 89 | this.graph = checkNotNull(graph); |
| 90 | this.src = checkNotNull(src); |
| 91 | this.dst = checkNotNull(dst); |
| 92 | this.weigher = checkNotNull(weigher); |
| 93 | |
| 94 | maskingWeigher = new InnerEdgeWeigher(weigher); |
| 95 | next = shortest.search(graph, src, dst, weigher, 1) |
| 96 | .paths().stream().findFirst().orElse(null); |
| 97 | } |
| 98 | |
| 99 | @Override |
| 100 | public boolean hasNext() { |
| 101 | return next != null; |
| 102 | } |
| 103 | |
| 104 | @Override |
| 105 | public Path<V, E> next() { |
| 106 | if (next == null) { |
| 107 | throw new NoSuchElementException("No more path between " + src + "-" + dst); |
| 108 | } |
| 109 | |
| 110 | // lastPath: the path to return at the end of this call |
| 111 | Path<V, E> lastPath = next; |
| 112 | resultPaths.add(lastPath); |
| 113 | |
| 114 | /// following is basically Yen's k-shortest path algorithm |
| 115 | |
| 116 | // start searching for next path |
| 117 | for (int i = 0; i < lastPath.edges().size(); i++) { |
| 118 | V spurNode = lastPath.edges().get(i).src(); |
| 119 | List<E> rootPathEdgeList = lastPath.edges().subList(0, i); |
| 120 | |
| 121 | for (Path<V, E> path : resultPaths) { |
| 122 | if (path.edges().size() >= i && |
| 123 | rootPathEdgeList.equals(path.edges().subList(0, i))) { |
| 124 | maskingWeigher.excluded.add(path.edges().get(i)); |
| 125 | } |
| 126 | } |
| 127 | |
| 128 | // Effectively remove all root path nodes other than spurNode |
| 129 | rootPathEdgeList.forEach(edge -> { |
| 130 | maskingWeigher.excluded.addAll(graph.getEdgesFrom(edge.src())); |
| 131 | maskingWeigher.excluded.addAll(graph.getEdgesTo(edge.src())); |
| 132 | }); |
| 133 | |
| 134 | shortest.search(graph, spurNode, dst, maskingWeigher, 1) |
| 135 | .paths().stream().findAny().ifPresent(spurPath -> { |
| 136 | List<E> totalPath = ImmutableList.<E>builder() |
| 137 | .addAll(rootPathEdgeList) |
| 138 | .addAll(spurPath.edges()) |
| 139 | .build(); |
| 140 | potentialPaths.add(path(totalPath)); |
| 141 | }); |
| 142 | |
| 143 | // Restore all removed paths and nodes |
| 144 | maskingWeigher.excluded.clear(); |
| 145 | } |
| 146 | |
| 147 | if (potentialPaths.isEmpty()) { |
| 148 | next = null; |
| 149 | } else { |
| 150 | next = potentialPaths.poll(); |
| 151 | } |
| 152 | |
| 153 | return lastPath; |
| 154 | } |
| 155 | |
| 156 | private Path<V, E> path(List<E> edges) { |
| 157 | //The following line must use the original weigher not the modified weigher because the modified |
| 158 | //weigher will count -1 values used for modifying the graph and return an inaccurate cost. |
| 159 | return new DefaultPath<>(edges, calculatePathCost(weigher, edges)); |
| 160 | } |
| 161 | |
| 162 | private Weight calculatePathCost(EdgeWeigher<V, E> weighter, List<E> edges) { |
| 163 | Weight totalCost = weighter.getInitialWeight(); |
| 164 | for (E edge : edges) { |
| 165 | totalCost = totalCost.merge(weighter.weight(edge)); |
| 166 | } |
| 167 | return totalCost; |
| 168 | } |
| 169 | } |
| 170 | |
| 171 | /** |
| 172 | * EdgeWeigher which excludes specified edges from path computation. |
| 173 | */ |
| 174 | private final class InnerEdgeWeigher implements EdgeWeigher<V, E> { |
| 175 | |
| 176 | private final Set<E> excluded = Sets.newConcurrentHashSet(); |
| 177 | private final EdgeWeigher<V, E> weigher; |
| 178 | |
| 179 | private InnerEdgeWeigher(EdgeWeigher<V, E> weigher) { |
| 180 | this.weigher = weigher; |
| 181 | } |
| 182 | |
| 183 | @Override |
| 184 | public Weight weight(E edge) { |
| 185 | if (excluded.contains(edge)) { |
| 186 | return weigher.getNonViableWeight(); |
| 187 | } |
| 188 | return weigher.weight(edge); |
| 189 | } |
| 190 | |
| 191 | @Override |
| 192 | public Weight getInitialWeight() { |
| 193 | return weigher.getInitialWeight(); |
| 194 | } |
| 195 | |
| 196 | @Override |
| 197 | public Weight getNonViableWeight() { |
| 198 | return weigher.getNonViableWeight(); |
| 199 | } |
| 200 | } |
| 201 | |
| 202 | /** |
| 203 | * Provides a comparator to order the set of paths. |
| 204 | * Compare by cost, then by hop count. |
| 205 | */ |
| 206 | private final class PathComparator implements Comparator<Path<V, E>> { |
| 207 | |
| 208 | @Override |
| 209 | public int compare(Path<V, E> pathOne, Path<V, E> pathTwo) { |
| 210 | return ComparisonChain.start() |
| 211 | .compare(pathOne.cost(), pathTwo.cost()) |
| 212 | .compare(pathOne.edges().size(), pathTwo.edges().size()) |
| 213 | .result(); |
| 214 | } |
| 215 | } |
| 216 | |
| 217 | } |