Package org.jgrapht.alg.shortestpath

Class ContractionHierarchyBidirectionalDijkstra<V,E>

java.lang.Object

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

Type Parameters:

V - the graph vertex type

E - the graph edge type

All Implemented Interfaces:

ShortestPathAlgorithm<V,E>

public class ContractionHierarchyBidirectionalDijkstra<V,E>
extends java.lang.Object

Implementation of the hierarchical query algorithm based on the bidirectional Dijkstra search. This algorithm is designed to contracted graphs. The best speedup is achieved on sparse graphs with low average outdegree.

The query algorithm is originally described the article: Robert Geisberger, Peter Sanders, Dominik Schultes, and Daniel Delling. 2008. Contraction hierarchies: faster and simpler hierarchical routing in road networks. In Proceedings of the 7th international conference on Experimental algorithms (WEA'08), Catherine C. McGeoch (Ed.). Springer-Verlag, Berlin, Heidelberg, 319-333.

During contraction graph is divided into 2 parts which are called upward and downward graphs. Both parts have all vertices of the original graph. The upward graph ($G_{\uparrow}$) contains only those edges which source has lower level than the target and vice versa for the downward graph ($G_{\downarrow}$).

For the shortest path query from $s$ to $t$, a modified bidirectional Dijkstra shortest path search is performed. The forward search from $s$ operates on $G_{\uparrow}$ and the backward search from $t$ - on the $G_{\downarrow}$. In each direction only the edges of the corresponding part of the graph are considered. Both searches eventually meet at the vertex $v$, which has the highest level in the shortest path from $s$ to $t$. Whenever a search in one direction reaches a vertex that has already been processed in other direction, a new candidate for a shortest path is found. Search is aborted in one direction if the smallest element in the corresponding priority queue is at least as large as the best candidate path found so far.

After computing a contracted path, the algorithm unpacks it recursively into the actual shortest path using the bypassed edges stored in the contraction hierarchy graph.

There is a possibility to provide an already computed contraction for the graph. For now there is no means to ensure that the specified contraction is correct, nor to fail-fast. If algorithm uses an incorrect contraction, the results of the search are unpredictable.

Since:

July 2019

Author:

Semen Chudakov

See Also:

ContractionHierarchyPrecomputation

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

Constructor Summary

Constructors

Constructor	Description
ContractionHierarchyBidirectionalDijkstra(ContractionHierarchyPrecomputation.ContractionHierarchy<V,E> hierarchy)	Constructs a new instance of the algorithm for a given hierarchy.
ContractionHierarchyBidirectionalDijkstra(ContractionHierarchyPrecomputation.ContractionHierarchy<V,E> hierarchy, double radius, java.util.function.Supplier<org.jheaps.AddressableHeap<java.lang.Double,Pair<ContractionHierarchyPrecomputation.ContractionVertex<V>,ContractionHierarchyPrecomputation.ContractionEdge<E>>>> heapSupplier)	Constructs a new instance of the algorithm for the given hierarchy, radius and heapSupplier.
ContractionHierarchyBidirectionalDijkstra(Graph<V,E> graph)	Constructs a new instance of the algorithm for a given graph.

Method Summary

Modifier and Type	Method	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 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 java.lang.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 java.lang.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 java.lang.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

ContractionHierarchyBidirectionalDijkstra

public ContractionHierarchyBidirectionalDijkstra(Graph<V,E> graph)

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

Parameters:

graph - the graph

ContractionHierarchyBidirectionalDijkstra

public ContractionHierarchyBidirectionalDijkstra(ContractionHierarchyPrecomputation.ContractionHierarchy<V,E> hierarchy)

Constructs a new instance of the algorithm for a given hierarchy.

Parameters:

hierarchy - contraction of the graph

ContractionHierarchyBidirectionalDijkstra

public ContractionHierarchyBidirectionalDijkstra(ContractionHierarchyPrecomputation.ContractionHierarchy<V,E> hierarchy,
                                                 double radius,
                                                 java.util.function.Supplier<org.jheaps.AddressableHeap<java.lang.Double,Pair<ContractionHierarchyPrecomputation.ContractionVertex<V>,ContractionHierarchyPrecomputation.ContractionEdge<E>>>> heapSupplier)

Constructs a new instance of the algorithm for the given hierarchy, radius and heapSupplier.

Parameters:

hierarchy - contraction of the graph

radius - search radius

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