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/*
* 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());
}
}
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