Package org.jgrapht.alg

Class KosarajuStrongConnectivityInspector<V,E>

java.lang.Object

org.jgrapht.alg.KosarajuStrongConnectivityInspector<V,E>

Type Parameters:

V - the graph vertex type

E - the graph edge type

All Implemented Interfaces:

StrongConnectivityAlgorithm<V,E>

public class KosarajuStrongConnectivityInspector<V,E>
extends java.lang.Object
implements StrongConnectivityAlgorithm<V,E>

Complements the ConnectivityInspector class with the capability to compute the strongly connected components of a directed graph. The algorithm is implemented after "Cormen et al: Introduction to agorithms", Chapter 22.5. It has a running time of O(V + E).

Unlike ConnectivityInspector, this class does not implement incremental inspection. The full algorithm is executed at the first call of stronglyConnectedSets() or isStronglyConnected().

Since:

Feb 2, 2005

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static class	KosarajuStrongConnectivityInspector.VertexData<V>
private static class	KosarajuStrongConnectivityInspector.VertexData1<V>
private static class	KosarajuStrongConnectivityInspector.VertexData2<V>

Field Summary

Fields

Modifier and Type	Field	Description
private DirectedGraph<V,E>	graph
private java.util.LinkedList<KosarajuStrongConnectivityInspector.VertexData<V>>	orderedVertices
private java.util.List<java.util.Set<V>>	stronglyConnectedSets
private java.util.List<DirectedSubgraph<V,E>>	stronglyConnectedSubgraphs
private java.util.Map<V,KosarajuStrongConnectivityInspector.VertexData<V>>	vertexToVertexData

Constructor Summary

Constructors

Constructor	Description
KosarajuStrongConnectivityInspector(DirectedGraph<V,E> directedGraph)	The constructor of the StrongConnectivityAlgorithm class.

Method Summary

Modifier and Type	Method	Description
private void	createVertexData()
private void	dfsVisit(DirectedGraph<V,E> visitedGraph, KosarajuStrongConnectivityInspector.VertexData<V> vertexData, java.util.Set<V> vertices)
DirectedGraph<V,E>	getGraph()	Returns the graph inspected by the StrongConnectivityAlgorithm.
boolean	isStronglyConnected()	Returns true if the graph of this StronglyConnectivityInspector instance is strongly connected.
private void	resetVertexData()
java.util.List<java.util.Set<V>>	stronglyConnectedSets()	Computes a List of Sets, where each set contains vertices which together form a strongly connected component within the given graph.
java.util.List<DirectedSubgraph<V,E>>	stronglyConnectedSubgraphs()	Computes a list of DirectedSubgraphs of the given graph.

Methods inherited from class java.lang.Object

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

Field Detail

graph

private final DirectedGraph<V,E> graph

orderedVertices

private java.util.LinkedList<KosarajuStrongConnectivityInspector.VertexData<V>> orderedVertices

stronglyConnectedSets

private java.util.List<java.util.Set<V>> stronglyConnectedSets

stronglyConnectedSubgraphs

private java.util.List<DirectedSubgraph<V,E>> stronglyConnectedSubgraphs

vertexToVertexData

private java.util.Map<V,KosarajuStrongConnectivityInspector.VertexData<V>> vertexToVertexData

Constructor Detail

KosarajuStrongConnectivityInspector

public KosarajuStrongConnectivityInspector(DirectedGraph<V,E> directedGraph)

The constructor of the StrongConnectivityAlgorithm class.

Parameters:

directedGraph - the graph to inspect

Throws:

java.lang.IllegalArgumentException - if the input graph is null

Method Detail

getGraph

public DirectedGraph<V,E> getGraph()

Returns the graph inspected by the StrongConnectivityAlgorithm.

Specified by:

getGraph in interface StrongConnectivityAlgorithm<V,E>

Returns:

the graph inspected by this StrongConnectivityAlgorithm

isStronglyConnected

public boolean isStronglyConnected()

Returns true if the graph of this StronglyConnectivityInspector instance is strongly connected.

Specified by:

isStronglyConnected in interface StrongConnectivityAlgorithm<V,E>

Returns:

true if the graph is strongly connected, false otherwise

stronglyConnectedSets

public java.util.List<java.util.Set<V>> stronglyConnectedSets()

Computes a List of Sets, where each set contains vertices which together form a strongly connected component within the given graph.

Specified by:

stronglyConnectedSets in interface StrongConnectivityAlgorithm<V,E>

Returns:

List of Set s containing the strongly connected components

stronglyConnectedSubgraphs

public java.util.List<DirectedSubgraph<V,E>> stronglyConnectedSubgraphs()

Computes a list of DirectedSubgraphs of the given graph. Each subgraph will represent a strongly connected component and will contain all vertices of that component. The subgraph will have an edge (u,v) iff u and v are contained in the strongly connected component.

NOTE: Calling this method will first execute stronglyConnectedSets(). If you don't need subgraphs, use that method.

Specified by:

stronglyConnectedSubgraphs in interface StrongConnectivityAlgorithm<V,E>

Returns:

a list of subgraphs representing the strongly connected components

createVertexData

private void createVertexData()

dfsVisit

private void dfsVisit(DirectedGraph<V,E> visitedGraph,
                      KosarajuStrongConnectivityInspector.VertexData<V> vertexData,
                      java.util.Set<V> vertices)

resetVertexData

private void resetVertexData()