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/*
* Copyright 2014-2015 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;
/**
* Bellman-Ford graph search algorithm for locating shortest-paths in
* directed graphs that may contain negative cycles.
*/
public class BellmanFordGraphSearch<V extends Vertex, E extends Edge<V>>
extends AbstractGraphPathSearch<V, E> {
@Override
public Result<V, E> search(Graph<V, E> graph, V src, V dst,
EdgeWeight<V, E> weight, int maxPaths) {
checkArguments(graph, src, dst);
// Prepare the graph search result.
DefaultResult result = new DefaultResult(src, dst, maxPaths);
// The source vertex has cost 0, of course.
result.updateVertex(src, null, 0.0, true);
int max = graph.getVertexes().size() - 1;
for (int i = 0; i < max; i++) {
// Relax, if possible, all egress edges of the current vertex.
for (E edge : graph.getEdges()) {
if (result.hasCost(edge.src())) {
result.relaxEdge(edge, result.cost(edge.src()), weight);
}
}
}
// Remove any vertexes reached by traversing edges with negative weights.
for (E edge : graph.getEdges()) {
if (result.hasCost(edge.src())) {
if (result.relaxEdge(edge, result.cost(edge.src()), weight)) {
result.removeVertex(edge.dst());
}
}
}
// Finally, but the paths on the search result and return.
result.buildPaths();
return result;
}
}
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