org.jgrapht.alg.shortestpath

Class FloydWarshallShortestPaths<V,E>

java.lang.Object

org.jgrapht.alg.shortestpath.FloydWarshallShortestPaths<V,E>

Type Parameters:

V - the graph vertex type

E - the graph edge type

All Implemented Interfaces:

ShortestPathAlgorithm<V,E>

public class FloydWarshallShortestPaths<V,E>
extends Object

The Floyd-Warshall algorithm.

The Floyd-Warshall algorithm finds all shortest paths (all $n^2$ of them) in $O(n^3)$ time. Note that during construction time, no computations are performed! All computations are performed the first time one of the member methods of this class is invoked. The results are stored, so all subsequent calls to the same method are computationally efficient.

Author:

Tom Larkworthy, Soren Davidsen (soren@tanesha.net), Joris Kinable, Dimitrios Michail

Nested Class Summary

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

ShortestPathAlgorithm.SingleSourcePaths<V,E>

Field Summary

Fields

Modifier and Type	Field and Description
protected Graph<V,E>	graph The underlying graph.
protected static String	GRAPH_CONTAINS_A_NEGATIVE_WEIGHT_CYCLE Error message for reporting the existence of a negative-weight cycle.
protected static String	GRAPH_MUST_CONTAIN_THE_SINK_VERTEX Error message for reporting that a sink vertex is missing.
protected static String	GRAPH_MUST_CONTAIN_THE_SOURCE_VERTEX Error message for reporting that a source vertex is missing.

Constructor Summary

Constructors

Constructor and Description
FloydWarshallShortestPaths(Graph<V,E> graph) Create a new instance of the Floyd-Warshall all-pairs shortest path algorithm.

Method Summary

Modifier and Type	Method and Description
protected GraphPath<V,E>	createEmptyPath(V source, V sink) Create an empty path.
V	getFirstHop(V a, V b) Returns the first hop, i.e., the second node on the shortest path from $a$ to $b$.
V	getLastHop(V a, V b) Returns the last hop, i.e., the second to last node on the shortest path from $a$ to $b$.
GraphPath<V,E>	getPath(V a, V b) Get a shortest path from a source vertex to a sink vertex.
ShortestPathAlgorithm.SingleSourcePaths<V,E>	getPaths(V source) Compute all shortest paths starting from a single source vertex.
double	getPathWeight(V source, V sink) Get the weight of the shortest path from a source vertex to a sink vertex.
int	getShortestPathsCount() Get the total number of shortest paths.

Methods inherited from class java.lang.Object

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

Field Detail

GRAPH_CONTAINS_A_NEGATIVE_WEIGHT_CYCLE

protected static final String GRAPH_CONTAINS_A_NEGATIVE_WEIGHT_CYCLE

Error message for reporting the existence of a negative-weight cycle.

See Also:

Constant Field Values

GRAPH_MUST_CONTAIN_THE_SOURCE_VERTEX

protected static final String GRAPH_MUST_CONTAIN_THE_SOURCE_VERTEX

Error message for reporting that a source vertex is missing.

See Also:

Constant Field Values

GRAPH_MUST_CONTAIN_THE_SINK_VERTEX

protected static final String GRAPH_MUST_CONTAIN_THE_SINK_VERTEX

Error message for reporting that a sink vertex is missing.

See Also:

Constant Field Values

graph

protected final Graph<V,E> graph

The underlying graph.

Constructor Detail

FloydWarshallShortestPaths

public FloydWarshallShortestPaths(Graph<V,E> graph)

Create a new instance of the Floyd-Warshall all-pairs shortest path algorithm.

Parameters:

graph - the input graph

Method Detail

getShortestPathsCount

public int getShortestPathsCount()

Get the total number of shortest paths. Does not count the paths from a vertex to itself.

Returns:

total number of shortest paths

getPath

public GraphPath<V,E> getPath(V a,
                              V b)

Get a shortest path from a source vertex to a sink vertex.

Parameters:

a - the source vertex

b - the target vertex

Returns:

a shortest path or null if no path exists

getPathWeight

public double getPathWeight(V source,
                            V sink)

Get the weight of the shortest path from a source vertex to a sink vertex. Returns Double.POSITIVE_INFINITY if no path exists.

Specified by:

getPathWeight in interface ShortestPathAlgorithm<V,E>

Parameters:

source - the source vertex

sink - the sink vertex

Returns:

the weight of the shortest path from a source vertex to a sink vertex, or Double.POSITIVE_INFINITY if no path exists

getPaths

public ShortestPathAlgorithm.SingleSourcePaths<V,E> getPaths(V source)

Compute all shortest paths starting from a single source vertex.

Specified by:

getPaths in interface ShortestPathAlgorithm<V,E>

Parameters:

source - the source vertex

Returns:

the shortest paths

getFirstHop

public V getFirstHop(V a,
                     V b)

Returns the first hop, i.e., the second node on the shortest path from $a$ to $b$. Lookup time is $O(1)$. If the shortest path from $a$ to $b$ is $a,c,d,e,b$, this method returns $c$. If the next invocation would query the first hop on the shortest path from $c$ to $b$, vertex $d$ would be returned, etc. This method is computationally cheaper than calling getPath(Object, Object) and then reading the first vertex.

Parameters:

a - source vertex

b - target vertex

Returns:

next hop on the shortest path from a to b, or null when there exists no path from $a$ to $b$.

getLastHop

public V getLastHop(V a,
                    V b)

Returns the last hop, i.e., the second to last node on the shortest path from $a$ to $b$. Lookup time is $O(1)$. If the shortest path from $a$ to $b$ is $a,c,d,e,b$, this method returns $e$. If the next invocation would query the next hop on the shortest path from $c$ to $e$, vertex $d$ would be returned, etc. This method is computationally cheaper than calling getPath(Object, Object) and then reading the vertex. The first invocation of this method populates a last hop matrix.

Parameters:

a - source vertex

b - target vertex

Returns:

last hop on the shortest path from $a$ to $b$, or null when there exists no path from $a$ to $b$.

createEmptyPath

protected final GraphPath<V,E> createEmptyPath(V source,
                                               V sink)

Create an empty path. Returns null if the source vertex is different than the target vertex.

Parameters:

source - the source vertex

sink - the sink vertex

Returns:

an empty path or null null if the source vertex is different than the target vertex