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. It can also calculate the graph diameter. 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

protected final Graph<V,E> 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
• getDiameter

public double getDiameter()
Compute the diameter of the graph.
Returns:
the diameter (longest of all the shortest paths) computed for the graph. If the graph contains no vertices, return Double.NaN. If there is no path between any two vertices, return Double.POSITIVE_INFINITY.
• 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