## Class CHManyToManyShortestPaths<V,​E>

• java.lang.Object
• org.jgrapht.alg.shortestpath.CHManyToManyShortestPaths<V,​E>
• Type Parameters:
V - the graph vertex type
E - the graph edge type
All Implemented Interfaces:
ManyToManyShortestPathsAlgorithm<V,​E>, ShortestPathAlgorithm<V,​E>

public class CHManyToManyShortestPaths<V,​E>
extends Object
Efficient algorithm for the many-to-many shortest paths problem based on contraction hierarchy.

The algorithm is originally described in the article: Sebastian Knopp, Peter Sanders, Dominik Schultes, Frank Schulz, and Dorothea Wagner. 2007. Computing many-to-many shortest paths using highway hierarchies. In Proceedings of the Meeting on Algorithm Engineering & Expermiments. Society for Industrial and Applied Mathematics, Philadelphia, PA, USA, 36-45.

First contraction hierarchy is constructed. Then for each target vertex a backward single source shortest paths search is performed on the contracted graph. During the searches a bucket $b(v)$ is associated with each vertex $v$ in the graph. A bucket stores a set of pairs $(t,d)$, where $t$ is a target vertex current search is performed from and $d$ is the computed distance from $v$ to this target. Then a forward single source shortest paths search is performed from every source vertex. When a search settles a vertex $v$ with distance $d(s,v)$, where $s$ is current source vertex, its bucket is scanned. For each entry $(t,d)$ if $d(s,t) > d(s,v) + d$ values of paths weight between $s$ and $t$ and its middle vertex is updated. The middle vertices are then used to restored actual path from the information in the shortest paths trees.

The efficiency of this algorithm is derived from the fact that contraction hierarchy produces fairly small shortest paths trees. This allows to both speedup the computations and decrease memory usage to store the paths.

Author:
Semen Chudakov
• ### Field Detail

• #### graph

protected final Graph<V,​E> graph
• ### Constructor Detail

• #### CHManyToManyShortestPaths

public CHManyToManyShortestPaths​(Graph<V,​E> graph)
Constructs an instance of the algorithm for a given graph.
Parameters:
graph - a graph
• #### CHManyToManyShortestPaths

public CHManyToManyShortestPaths​(ContractionHierarchyPrecomputation.ContractionHierarchy<V,​E> contractionHierarchy)
Constructs an instance of the algorithm for a given contractionHierarchy.
Parameters:
contractionHierarchy - contraction of the graph
• ### Method Detail

• #### getManyToManyPaths

public ManyToManyShortestPathsAlgorithm.ManyToManyShortestPaths<V,​E> getManyToManyPaths​(Set<V> sources,
Set<V> targets)
Computes shortest paths from all vertices in sources to all vertices in targets.
Parameters:
sources - list of sources vertices
targets - list of target vertices
Returns:
computed shortest paths
• #### getPath

public GraphPath<V,​E> getPath​(V source,
V sink)
Get a shortest path from a source vertex to a sink vertex.
Specified by:
getPath in interface ShortestPathAlgorithm<V,​E>
Parameters:
source - the source vertex
sink - 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
• #### getShortestPathsTree

protected static <V,​E> ShortestPathAlgorithm.SingleSourcePaths<V,​E> getShortestPathsTree​(Graph<V,​E> graph,
V source,
Set<V> targets)
Computes shortest paths tree starting at source and stopping as soon as all of the targets are reached. Here the DijkstraClosestFirstIterator is used.
Type Parameters:
V - the graph vertex type
E - the graph edge type
Parameters:
graph - a graph
source - source vertex
targets - target vertices
Returns:
shortest paths starting from source and reaching all targets