Package org.jgrapht.alg.shortestpath

Class 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

    • 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

      • 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