Package ghidra.graph.algo

Class DijkstraShortestPathsAlgorithm.OneSourceToAll

  • Enclosing class:
    DijkstraShortestPathsAlgorithm<V,​E extends GEdge<V>>
    protected class DijkstraShortestPathsAlgorithm.OneSourceToAll
extends java.lang.Object
    A class representing all optimal paths from a given source to every other (reachable) vertex in the graph

    This is the workhorse of path computation, and implements Dijkstra's Shortest Path algorithm from one source to all destinations. We considered using JUNG to store the graph and compute the paths, but we could not, because we would like to find all paths having the optimal distance. If there are ties, JUNG's implementation chooses one arbitrarily; we would like all tied paths.

    • Constructor Summary

      Constructors 
      Modifier Constructor Description
      protected OneSourceToAll​(V src)
      Compute the shortest paths from a given vertex to all other reachable vertices in the graph

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      protected boolean addOrUpdate​(V dest, double newDist)
      Update the record for the given destination with a new offer of shortest distance
      protected void addPathsTo​(java.util.Collection<java.util.Deque<E>> paths, V dst)
      Add the shortest paths from the source to the given destination into the given collection
      protected void addPathsTo​(java.util.Collection<java.util.Deque<E>> paths, V prev, java.util.Deque<E> soFar)
      Add the shortest paths from source to a given intermediate, continuing along a given path to the final destination, into the given collection
      java.util.Collection<java.util.Deque<E>> computeOptimalPathsTo​(V dst)
      Recover the shortest paths from the source to the given destination, if it is reachable
      protected void fill()
      Compute paths, building out the graph until all reachable vertices have been visited
      protected void fillStep​(V from, double dist)
      Perform one iteration of Dijskstra's path finding algorithm

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • queueByDistance

        protected final ValueSortedMap<V,​java.lang.Double> queueByDistance

      • visitedDistance

        protected final java.util.Map<V,​java.lang.Double> visitedDistance

      • bestIns

        protected final java.util.Map<V,​java.util.Set<E extends GEdge<V>>> bestIns

      • source

        protected final V source

    • Constructor Detail

      • OneSourceToAll

        protected OneSourceToAll​(V src)
        Compute the shortest paths from a given vertex to all other reachable vertices in the graph
        Parameters:
        src - the source (seed) vertex

    • Method Detail

      • computeOptimalPathsTo

        public java.util.Collection<java.util.Deque<E>> computeOptimalPathsTo​(V dst)
        Recover the shortest paths from the source to the given destination, if it is reachable
        Parameters:
        dst - the destination
        Returns:
        a collection of the shortest paths from source to destination, or the empty set

      • addPathsTo

        protected void addPathsTo​(java.util.Collection<java.util.Deque<E>> paths,
                          V dst)
        Add the shortest paths from the source to the given destination into the given collection

        This is used internally to recover the shortest paths

        Parameters:
        paths - a place to store the recovered paths
        dst - the destination

      • addPathsTo

        protected void addPathsTo​(java.util.Collection<java.util.Deque<E>> paths,
                          V prev,
                          java.util.Deque<E> soFar)
        Add the shortest paths from source to a given intermediate, continuing along a given path to the final destination, into the given collection

        This is a recursive method for constructing the shortest paths overall. Assuming the given path from intermediate to final destination is the shortest, we can show by induction, the computed paths from source to destination are the shortest.

        Parameters:
        paths - a place to store the recovered paths
        prev - the intermediate destination
        soFar - a (shortest) path from intermediate to final destination

      • addOrUpdate

        protected boolean addOrUpdate​(V dest,
                              double newDist)
        Update the record for the given destination with a new offer of shortest distance

        If either the record doesn't exist yet, or the new offer beats the current best, then a new record is created and replaces the current record. If present, the list of best inbound edges is cleared -- because they all correspond to a distance that has just been beat. The node is also added and/or moved forward in the queue of unvisited vertices.

        If the record exists, and the new offer ties the current offer, nothing happens, but the method still returns true, since the corresponding inbound edge could be optimal.

        If the record's current best beats the offer, nothing happens, and the method returns false, indicating the inbound edge is definitely not optimal.

        Parameters:
        dest - the destination whose record to update
        newDist - the distance offer
        Returns:
        true iff the offer is equal to or better than the record's current best

      • fill

        protected void fill()
        Compute paths, building out the graph until all reachable vertices have been visited

      • fillStep

        protected void fillStep​(V from,
                        double dist)
        Perform one iteration of Dijskstra's path finding algorithm
        Parameters:
        from - the vertex to visit for this iteration