Thomas Vachuska | 24c849c | 2014-10-27 09:53:05 -0700 | [diff] [blame] | 1 | /* |
Brian O'Connor | 5ab426f | 2016-04-09 01:19:45 -0700 | [diff] [blame] | 2 | * Copyright 2014-present Open Networking Laboratory |
Thomas Vachuska | 24c849c | 2014-10-27 09:53:05 -0700 | [diff] [blame] | 3 | * |
Thomas Vachuska | 4f1a60c | 2014-10-28 13:39:07 -0700 | [diff] [blame] | 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 |
Thomas Vachuska | 24c849c | 2014-10-27 09:53:05 -0700 | [diff] [blame] | 7 | * |
Thomas Vachuska | 4f1a60c | 2014-10-28 13:39:07 -0700 | [diff] [blame] | 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. |
Thomas Vachuska | 24c849c | 2014-10-27 09:53:05 -0700 | [diff] [blame] | 15 | */ |
tom | 2e1f071 | 2014-08-29 13:32:00 -0700 | [diff] [blame] | 16 | package org.onlab.graph; |
| 17 | |
| 18 | /** |
| 19 | * Bellman-Ford graph search algorithm for locating shortest-paths in |
| 20 | * directed graphs that may contain negative cycles. |
| 21 | */ |
| 22 | public class BellmanFordGraphSearch<V extends Vertex, E extends Edge<V>> |
| 23 | extends AbstractGraphPathSearch<V, E> { |
| 24 | |
| 25 | @Override |
Andrey Komarov | 2398d96 | 2016-09-26 15:11:23 +0300 | [diff] [blame] | 26 | protected Result<V, E> internalSearch(Graph<V, E> graph, V src, V dst, |
| 27 | EdgeWeigher<V, E> weigher, int maxPaths) { |
tom | 2e1f071 | 2014-08-29 13:32:00 -0700 | [diff] [blame] | 28 | |
| 29 | // Prepare the graph search result. |
Thomas Vachuska | c31d9f1 | 2015-01-22 12:33:27 -0800 | [diff] [blame] | 30 | DefaultResult result = new DefaultResult(src, dst, maxPaths); |
tom | 2e1f071 | 2014-08-29 13:32:00 -0700 | [diff] [blame] | 31 | |
| 32 | // The source vertex has cost 0, of course. |
Andrey Komarov | 2398d96 | 2016-09-26 15:11:23 +0300 | [diff] [blame] | 33 | result.updateVertex(src, null, weigher.getInitialWeight(), true); |
tom | 2e1f071 | 2014-08-29 13:32:00 -0700 | [diff] [blame] | 34 | |
| 35 | int max = graph.getVertexes().size() - 1; |
| 36 | for (int i = 0; i < max; i++) { |
| 37 | // Relax, if possible, all egress edges of the current vertex. |
| 38 | for (E edge : graph.getEdges()) { |
| 39 | if (result.hasCost(edge.src())) { |
Andrey Komarov | 2398d96 | 2016-09-26 15:11:23 +0300 | [diff] [blame] | 40 | result.relaxEdge(edge, result.cost(edge.src()), weigher); |
tom | 2e1f071 | 2014-08-29 13:32:00 -0700 | [diff] [blame] | 41 | } |
| 42 | } |
| 43 | } |
| 44 | |
| 45 | // Remove any vertexes reached by traversing edges with negative weights. |
| 46 | for (E edge : graph.getEdges()) { |
| 47 | if (result.hasCost(edge.src())) { |
Andrey Komarov | 2398d96 | 2016-09-26 15:11:23 +0300 | [diff] [blame] | 48 | if (result.relaxEdge(edge, result.cost(edge.src()), weigher)) { |
tom | 2e1f071 | 2014-08-29 13:32:00 -0700 | [diff] [blame] | 49 | result.removeVertex(edge.dst()); |
| 50 | } |
| 51 | } |
| 52 | } |
| 53 | |
| 54 | // Finally, but the paths on the search result and return. |
| 55 | result.buildPaths(); |
| 56 | return result; |
| 57 | } |
tom | 2e1f071 | 2014-08-29 13:32:00 -0700 | [diff] [blame] | 58 | } |