Class DijkstraIterator
Object
AbstractGraphIterator
SourceGraphIterator
DijkstraIterator
- All Implemented Interfaces:
GraphIterator
- Direct Known Subclasses:
DirectedDijkstraIterator
Iterates over the nodes of a graph in pattern using Dijkstra's Shortest Path Algorithm. A Dijkstra iteration
returns nodes in an order of increasing cost relative to a specified node (the source node of the iteration).
In a Dijkstra iteration, a weight is associated with each edge and a cost with each node. The iteration operates by maintaining two sets of nodes. The first the set of nodes whose final cost is known, and the second is the set of nodes whose final cost is unknown. Initially, every node except for the source node has a cost of infinity, and resides in the unknown set. The source node has a cost of zero, and is is a member of the known set.
The iteration operates as follows:
The nodes are returned in order of increasing cost which yields the sequence A,C,B,D,E,F,G,H,I.
In a Dijkstra iteration, a weight is associated with each edge and a cost with each node. The iteration operates by maintaining two sets of nodes. The first the set of nodes whose final cost is known, and the second is the set of nodes whose final cost is unknown. Initially, every node except for the source node has a cost of infinity, and resides in the unknown set. The source node has a cost of zero, and is is a member of the known set.
The iteration operates as follows:
sn = source node of iteration N = set of all nodes K = set of nodes with known cost = {sn} U = set of nodes with unknown cost = N - K cost(sn) = 0 for each node $un in U cost(un) = infinity while(|U| > 0) for each node n in K find a node un in U that relates to n if cost(n) + weight(n,un) < cost(un) cost(un) = cost(n) + weight(n,un) ln = node with least cost in U remove ln from U add ln to K return ln as next node in iterationThe following is an illustration of the algorithm. Edge weights are labelled in blue and the final node costs are labelled in red.

The nodes are returned in order of increasing cost which yields the sequence A,C,B,D,E,F,G,H,I.
- Author:
- Justin Deoliveira, Refractions Research Inc, jdeolive@refractions.net
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionprotected static class
Internal data structure used to track node costs, and parent nodes.static interface
Supplies a weight for each edge in the graph to be used by the iteration when calculating node costs.static interface
Supplies a weight for each pair of adjacent edges. -
Field Summary
FieldsModifier and TypeFieldDescriptionprotected HashMap<Graphable,
DijkstraIterator.DijkstraNode> map of graph node to internal Dijkstra node *protected DijkstraIterator.NodeWeighter
provides weights for nodes in the graph *protected PriorityQueue<DijkstraIterator.DijkstraNode>
priority queue to manage active nodes *protected DijkstraIterator.EdgeWeighter
provides weights for edges in the graph * -
Constructor Summary
ConstructorsConstructorDescriptionConstructs a new Dijkstra iterator which uses the specified EdgeWeighter.DijkstraIterator
(DijkstraIterator.EdgeWeighter weighter, DijkstraIterator.NodeWeighter nweighter) Constructs a new Dijkstra iterator which uses the specified EdgeWeighter and NodeWeighter -
Method Summary
Modifier and TypeMethodDescriptionvoid
cont
(Graphable current, GraphTraversal traversal) Looks for adjacent nodes to the current node which are in the adjacent node and updates costs.double
Returns the internal cost of a node which has been calculated by the iterator.Returns the last node in the known set to update the node.protected PriorityQueue
getQueue()
getRelated
(Graphable current) void
init
(Graph graph, GraphTraversal traversal) Builds internal priority queue to manage node costs.void
killBranch
(Graphable current, GraphTraversal traversal) Kills the branch of the traversal by not updating the cost of any adjacent nodes.next
(GraphTraversal traversal) Returns the next node in the priority queue.Methods inherited from class SourceGraphIterator
getSource, setSource
Methods inherited from class AbstractGraphIterator
getGraph, getTraversal, getWalker, setTraversal
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Field Details
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weighter
provides weights for edges in the graph * -
nweighter
provides weights for nodes in the graph * -
queue
priority queue to manage active nodes * -
nodemap
map of graph node to internal Dijkstra node *
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Constructor Details
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DijkstraIterator
Constructs a new Dijkstra iterator which uses the specified EdgeWeighter.- Parameters:
weighter
- Calculates weights for edges in the graph being iterated over.
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DijkstraIterator
public DijkstraIterator(DijkstraIterator.EdgeWeighter weighter, DijkstraIterator.NodeWeighter nweighter) Constructs a new Dijkstra iterator which uses the specified EdgeWeighter and NodeWeighter- Parameters:
weighter
- Calculates weights for edges in the graph being iterated over.nweighter
- Calculates weights for nodes in the graph being iterated over.
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Method Details
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init
Builds internal priority queue to manage node costs.- Parameters:
graph
- The graph being whose components are being iterated over.- See Also:
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org.geotools.graph.traverse.GraphIterator#init(Graph)
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next
Returns the next node in the priority queue. If the next node coming out of the queue has infinite cost, then the node is not adjacent to any nodes in the set of nodes with known costs. This situation will end the traversal every other node will also have infinite cost. This usually is the result of a disconnected graph.- Returns:
- The next component in the iteration, or null if iteration is complete.
- See Also:
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org.geotools.graph.traverse.GraphIterator#next()
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cont
Looks for adjacent nodes to the current node which are in the adjacent node and updates costs.- Parameters:
current
- The current component of the traversal.- See Also:
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org.geotools.graph.traverse.GraphIterator#cont(Graphable)
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killBranch
Kills the branch of the traversal by not updating the cost of any adjacent nodes.- Parameters:
current
- The current component of the traversal.- See Also:
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org.geotools.graph.traverse.GraphIterator#killBranch(Graphable)
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getCost
Returns the internal cost of a node which has been calculated by the iterator.- Parameters:
component
- The component whose cost to return.- Returns:
- The cost associated with the component.
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getParent
Returns the last node in the known set to update the node. The iteration operates by nodes in the known set updating the cost of nodes in the unknown set. Each time an update occurs, the known node is set as the parent of the unkown node.- Parameters:
component
- The node whose parent to return (child)- Returns:
- The parent, or null if the method is supplied the source of the iteration.
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getQueue
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getRelated
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