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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;
import java.util.HashSet;
import java.util.Set;
/**
* Implementation of the BFS algorithm.
*/
public class BreadthFirstSearch<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 result.
DefaultResult result = new DefaultResult(src, dst, maxPaths);
// Setup the starting frontier with the source as the sole vertex.
Set<V> frontier = new HashSet<>();
result.updateVertex(src, null, 0.0, true);
frontier.add(src);
boolean reachedEnd = false;
while (!reachedEnd && !frontier.isEmpty()) {
// Prepare the next frontier.
Set<V> next = new HashSet<>();
// Visit all vertexes in the current frontier.
for (V vertex : frontier) {
double cost = result.cost(vertex);
// Visit all egress edges of the current frontier vertex.
for (E edge : graph.getEdgesFrom(vertex)) {
V nextVertex = edge.dst();
if (!result.hasCost(nextVertex)) {
// If this vertex has not been visited yet, update it.
double newCost = cost + (weight == null ? 1.0 : weight.weight(edge));
result.updateVertex(nextVertex, edge, newCost, true);
// If we have reached our intended destination, bail.
if (nextVertex.equals(dst)) {
reachedEnd = true;
break;
}
next.add(nextVertex);
}
if (reachedEnd) {
break;
}
}
}
// Promote the next frontier.
frontier = next;
}
// Finally, but the paths on the search result and return.
result.buildPaths();
return result;
}
}
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