org.jgrapht.alg.shortestpath

Class BidirectionalAStarShortestPath<V,E>

java.lang.Object

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

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

Type Parameters:

V - the graph vertex type

E - the graph edge type

All Implemented Interfaces:

ShortestPathAlgorithm<V,E>

public class BidirectionalAStarShortestPath<V,E>
extends BaseBidirectionalShortestPathAlgorithm<V,E>

A bidirectional version of A* algorithm.

See the Wikipedia article for details and references about bidirectional search. This technique does not change the worst-case behavior of the algorithm but reduces, in some cases, the number of visited vertices in practice.

The algorithm was first introduced in Ira Sheldon Pohl. 1969. Bi-Directional and Heuristic Search in Path Problems. Ph.D. Dissertation. Stanford University, Stanford, CA, USA. AAI7001588.

The implementation uses two termination criteria depending on if the provided heuristic is consistent or not. Both criteria are based on the shortest path distance $\mu$ seen thus far in the search. Initially, in both cases the algorithm sets $\mu=\infty$. Whenever the search updates the information about the vertex $v$, it sets $\mu = min\{\mu; g_f(v) + g_b(v)\}$, where $g_f(v)$ is the current best-known path cost from $source$ to $sink$ and $g_b(v)$ is the current best-known path cost from $sink$ to $source$.

Author:

Semen Chudakov, Dimitrios Michail, Joris Kinable, Jon Robison, Thomas Breitbart

See Also:

AStarShortestPath

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
BidirectionalAStarShortestPath(Graph<V,E> graph, AStarAdmissibleHeuristic<V> heuristic) Constructs a new instance of the algorithm for a given graph and heuristic.
BidirectionalAStarShortestPath(Graph<V,E> graph, AStarAdmissibleHeuristic<V> heuristic, Supplier<org.jheaps.AddressableHeap<Double,V>> heapSupplier) Constructs a new instance of the algorithm for a given graph, heuristic and heap supplier.

Method Summary

Modifier and Type	Method and Description
protected GraphPath<V,E>	createEmptyPath(V source, V sink) Create an empty path.
GraphPath<V,E>	getPath(V source, V sink) 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.

Methods inherited from class org.jgrapht.alg.shortestpath.BaseBidirectionalShortestPathAlgorithm

createPath

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

BidirectionalAStarShortestPath

public BidirectionalAStarShortestPath(Graph<V,E> graph,
                                      AStarAdmissibleHeuristic<V> heuristic)

Constructs a new instance of the algorithm for a given graph and heuristic.

Parameters:

graph - the graph

heuristic - heuristic that estimates distances between nodes

BidirectionalAStarShortestPath

public BidirectionalAStarShortestPath(Graph<V,E> graph,
                                      AStarAdmissibleHeuristic<V> heuristic,
                                      Supplier<org.jheaps.AddressableHeap<Double,V>> heapSupplier)

Constructs a new instance of the algorithm for a given graph, heuristic and heap supplier.

Parameters:

graph - the graph

heuristic - heuristic that estimates distances between nodes

heapSupplier - supplier of the preferable heap implementation

Method Detail

getPath

public GraphPath<V,E> getPath(V source,
                              V sink)

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

Parameters:

source - the source vertex

sink - the target vertex

Returns:

a shortest path or null 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

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

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