org.jgrapht.alg.shortestpath.YenKShortestPath Maven / Gradle / Ivy
/*
* (C) Copyright 2019-2023, by Semen Chudakov and Contributors.
*
* JGraphT : a free Java graph-theory library
*
* See the CONTRIBUTORS.md file distributed with this work for additional
* information regarding copyright ownership.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License 2.0 which is available at
* http://www.eclipse.org/legal/epl-2.0, or the
* GNU Lesser General Public License v2.1 or later
* which is available at
* http://www.gnu.org/licenses/old-licenses/lgpl-2.1-standalone.html.
*
* SPDX-License-Identifier: EPL-2.0 OR LGPL-2.1-or-later
*/
package org.jgrapht.alg.shortestpath;
import org.jgrapht.*;
import org.jgrapht.alg.interfaces.*;
import java.util.*;
/**
* Implementation of Yen`s algorithm for finding $k$ shortest loopless paths.
*
*
* The time complexity of the algorithm is $O(kn(m + n log n))$, where $n$ is the number of vertices
* in the graph, $m$ is the number of edges in the graph and $k$ is the number of paths needed.
*
*
* The algorithm is originally described in: Q. V. Martins, Ernesto and M. B. Pascoal, Marta.
* (2003). A new implementation of Yen’s ranking loopless paths algorithm. Quarterly Journal of the
* Belgian, French and Italian Operations Research Societies. 1. 121-133. 10.1007/s10288-002-0010-2.
*
*
* The implementation iterates over the existing loopless path between the {@code source} and the
* {@code sink} and forms the resulting list. It is possible to provide a {@link PathValidator} to
* filter the resulting path list
*
* @param the graph vertex type
* @param the graph edge type
* @author Semen Chudakov
* @see YenShortestPathIterator
* @see PathValidator
*/
public class YenKShortestPath
implements KShortestPathAlgorithm
{
/**
* Underlying graph.
*/
private final Graph graph;
/**
* Provides validation for the paths which will be computed. If the validator is {@code null},
* this means that all paths are valid.
*/
private PathValidator pathValidator;
/**
* Constructs an instance of the algorithm for the given {@code graph}.
*
* @param graph graph
*/
public YenKShortestPath(Graph graph)
{
this(graph, null);
}
/**
* Constructs an instance of the algorithm for the given {@code graph} and
* {@code pathValidator}.
*
* @param graph graph
* @param pathValidator validator for computed paths
*/
public YenKShortestPath(Graph graph, PathValidator pathValidator)
{
this.graph = Objects.requireNonNull(graph, "Graph cannot be null!");
this.pathValidator = pathValidator;
}
/**
* Computes {@code k} shortest loopless paths between {@code source} and {@code sink}. If the
* overall number of such paths is denoted by $n$, the method returns $m = min\{k, n\}$ such
* paths. The paths are produced in sorted order by weights.
*
* @param source the source vertex
* @param sink the target vertex
* @param k the number of shortest paths to return
* @return a list of k shortest paths
*/
@Override
public List> getPaths(V source, V sink, int k)
{
if (k < 0) {
throw new IllegalArgumentException("k should be positive");
}
List> result = new ArrayList<>();
YenShortestPathIterator iterator =
new YenShortestPathIterator<>(graph, source, sink, pathValidator);
for (int i = 0; i < k && iterator.hasNext(); i++) {
result.add(iterator.next());
}
return result;
}
}