Class ClosestFirstIterator<V,​E>

  • Type Parameters:
    V - the graph vertex type
    E - the graph edge type
    All Implemented Interfaces:
    java.util.Iterator<V>, GraphIterator<V,​E>

    public class ClosestFirstIterator<V,​E>
    extends CrossComponentIterator<V,​E,​FibonacciHeapNode<ClosestFirstIterator.QueueEntry<V,​E>>>
    A closest-first iterator for a directed or undirected graph. For this iterator to work correctly the graph must not be modified during iteration. Currently there are no means to ensure that, nor to fail-fast. The results of such modifications are undefined.

    The metric for closest here is the weighted path length from a start vertex, i.e. Graph.getEdgeWeight(Edge) is summed to calculate path length. Negative edge weights will result in an IllegalArgumentException. Optionally, path length may be bounded by a finite radius.

    Since:
    Sep 2, 2003
    • Constructor Detail

      • ClosestFirstIterator

        public ClosestFirstIterator​(Graph<V,​E> g)
        Creates a new closest-first iterator for the specified graph.
        Parameters:
        g - the graph to be iterated.
      • ClosestFirstIterator

        public ClosestFirstIterator​(Graph<V,​E> g,
                                    V startVertex)
        Creates a new closest-first iterator for the specified graph. Iteration will start at the specified start vertex and will be limited to the connected component that includes that vertex. If the specified start vertex is null, iteration will start at an arbitrary vertex and will not be limited, that is, will be able to traverse all the graph.
        Parameters:
        g - the graph to be iterated.
        startVertex - the vertex iteration to be started.
      • ClosestFirstIterator

        public ClosestFirstIterator​(Graph<V,​E> g,
                                    V startVertex,
                                    double radius)
        Creates a new radius-bounded closest-first iterator for the specified graph. Iteration will start at the specified start vertex and will be limited to the subset of the connected component which includes that vertex and is reachable via paths of weighted length less than or equal to the specified radius. The specified start vertex may not be null.
        Parameters:
        g - the graph to be iterated.
        startVertex - the vertex iteration to be started.
        radius - limit on weighted path length, or Double.POSITIVE_INFINITY for unbounded search.
    • Method Detail

      • setCrossComponentTraversal

        public void setCrossComponentTraversal​(boolean crossComponentTraversal)
        Description copied from class: AbstractGraphIterator
        Sets the cross component traversal flag - indicates whether to traverse the graph across connected components.
        Overrides:
        setCrossComponentTraversal in class AbstractGraphIterator<V,​E>
        Parameters:
        crossComponentTraversal - if true traverses across connected components.
      • getShortestPathLength

        public double getShortestPathLength​(V vertex)
        Get the weighted length of the shortest path known to the given vertex. If the vertex has already been visited, then it is truly the shortest path length; otherwise, it is the best known upper bound.
        Parameters:
        vertex - vertex being sought from start vertex
        Returns:
        weighted length of shortest path known, or Double.POSITIVE_INFINITY if no path found yet
      • getSpanningTreeEdge

        public E getSpanningTreeEdge​(V vertex)
        Get the spanning tree edge reaching a vertex which has been seen already in this traversal. This edge is the last link in the shortest known path between the start vertex and the requested vertex. If the vertex has already been visited, then it is truly the minimum spanning tree edge; otherwise, it is the best candidate seen so far.
        Parameters:
        vertex - the spanned vertex.
        Returns:
        the spanning tree edge, or null if the vertex either has not been seen yet or is the start vertex.
      • assertNonNegativeEdge

        private void assertNonNegativeEdge​(E edge)
      • calculatePathLength

        private double calculatePathLength​(V vertex,
                                           E edge)
        Determine weighted path length to a vertex via an edge, using the path length for the opposite vertex.
        Parameters:
        vertex - the vertex for which to calculate the path length.
        edge - the edge via which the path is being extended.
        Returns:
        calculated path length.
      • checkRadiusTraversal

        private void checkRadiusTraversal​(boolean crossComponentTraversal)
      • createSeenData

        private FibonacciHeapNode<ClosestFirstIterator.QueueEntry<V,​E>> createSeenData​(V vertex,
                                                                                             E edge)
        The first time we see a vertex, make up a new heap node for it.
        Parameters:
        vertex - a vertex which has just been encountered.
        edge - the edge via which the vertex was encountered.
        Returns:
        the new heap node.