org.jgrapht.alg.vertexcover

Class GreedyVCImpl<V,E>

java.lang.Object

org.jgrapht.alg.vertexcover.GreedyVCImpl<V,E>

Type Parameters:

V - the graph vertex type

E - the graph edge type

All Implemented Interfaces:

VertexCoverAlgorithm<V>

public class GreedyVCImpl<V,E>
extends Object
implements VertexCoverAlgorithm<V>

Greedy algorithm to find a vertex cover for a graph. A vertex cover is a set of vertices that touches all the edges in the graph. The graph's vertex set is a trivial cover. However, a minimal vertex set (or at least an approximation for it) is usually desired. Finding a true minimal vertex cover is an NP-Complete problem. For more on the vertex cover problem, see http://mathworld.wolfram.com/VertexCover.html Note: this class supports pseudo-graphs Runtime: $O(|E| \log |V|)$ This class produces often, but not always, better solutions than the 2-approximation algorithms. Nevertheless, there are instances where the solution is significantly worse. In those cases, consider using ClarksonTwoApproxVCImpl.

Author:

Joris Kinable

Nested Class Summary

Nested classes/interfaces inherited from interface org.jgrapht.alg.interfaces.VertexCoverAlgorithm

VertexCoverAlgorithm.VertexCover<V>, VertexCoverAlgorithm.VertexCoverImpl<V>

Constructor Summary

Constructors

Constructor and Description
GreedyVCImpl(Graph<V,E> graph) Constructs a new GreedyVCImpl instance where all vertices have uniform weights.
GreedyVCImpl(Graph<V,E> graph, Map<V,Double> vertexWeightMap) Constructs a new GreedyVCImpl instance

Method Summary

Modifier and Type	Method and Description
VertexCoverAlgorithm.VertexCover<V>	getVertexCover() Finds a greedy solution to the minimum weighted vertex cover problem.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GreedyVCImpl

public GreedyVCImpl(Graph<V,E> graph)

Constructs a new GreedyVCImpl instance where all vertices have uniform weights.

Parameters:

graph - input graph

GreedyVCImpl

public GreedyVCImpl(Graph<V,E> graph,
                    Map<V,Double> vertexWeightMap)

Constructs a new GreedyVCImpl instance

Parameters:

graph - input graph

vertexWeightMap - mapping of vertex weights

Method Detail

getVertexCover

public VertexCoverAlgorithm.VertexCover<V> getVertexCover()

Finds a greedy solution to the minimum weighted vertex cover problem. At each iteration, the algorithm picks the vertex v with the smallest ratio weight(v)/degree(v) and adds it to the cover. Next vertex v and all edges incident to it are removed. The process repeats until all vertices are covered. Runtime: O(|E|*log|V|)

Specified by:

getVertexCover in interface VertexCoverAlgorithm<V>

Returns:

greedy solution