Package org.jgrapht.alg.shortestpath

Class 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

    • 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

      • 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