Class FloydWarshallShortestPaths<V,E>

java.lang.Object
org.jgrapht.alg.shortestpath.BaseShortestPathAlgorithm<V,E>
org.jgrapht.alg.shortestpath.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 BaseShortestPathAlgorithm<V,E>
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.

  • Field Details

    • vertices

      private final List<V> vertices
    • degrees

      private final List<Integer> degrees
    • vertexIndices

      private final Map<V,Integer> vertexIndices
    • minDegreeOne

      private final int minDegreeOne
    • minDegreeTwo

      private final int minDegreeTwo
    • d

      private double[][] d
    • backtrace

      private Object[][] backtrace
    • lastHopMatrix

      private Object[][] lastHopMatrix
  • Constructor Details

    • 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 Details

    • 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>
      Overrides:
      getPathWeight in class BaseShortestPathAlgorithm<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
    • 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>
      Overrides:
      getPaths in class BaseShortestPathAlgorithm<V,E>
      Parameters:
      source - the source vertex
      Returns:
      the shortest paths
    • 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 $b$.
    • lazyCalculateMatrix

      private void lazyCalculateMatrix()
      Calculates the matrix of all shortest paths, but does not populate the last hops matrix.
    • populateLastHopMatrix

      private void populateLastHopMatrix()
      Populate the last hop matrix, using the earlier computed backtrace matrix.