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. 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

• ### Nested classes/interfaces inherited from interface org.jgrapht.alg.interfaces.ShortestPathAlgorithm

ShortestPathAlgorithm.SingleSourcePaths<V,E>
• ### Field Summary

Fields
Modifier and Type Field and Description
protected Graph<V,E> graph
The underlying graph.
• ### Constructor Summary

Constructors
Constructor and Description
FloydWarshallShortestPaths(Graph<V,E> graph)
Create a new instance of the Floyd-Warshall all-pairs shortest path algorithm.
• ### Method Summary

All Methods
Modifier and Type Method and Description
protected GraphPath<V,E> createEmptyPath(V source, V sink)
Create an empty path.
V getFirstHop(V a, V b)
Returns the first hop, i.e., the second node on the shortest path from $a$ to $b$.
V getLastHop(V a, V b)
Returns the last hop, i.e., the second to last node on the shortest path from $a$ to $b$.
GraphPath<V,E> getPath(V a, V b)
Get a shortest path from a source vertex to a sink vertex.
ShortestPathAlgorithm.SingleSourcePaths<V,E> getPaths(V source)
Compute all shortest paths starting from a single source vertex.
double getPathWeight(V source, V sink)
Get the weight of the shortest path from a source vertex to a sink vertex.
int getShortestPathsCount()
Get the total number of shortest paths.
• ### Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
• ### Field Detail

• #### graph

protected final Graph<V,E> graph
The underlying 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
• #### 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
• #### 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>
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 $b$.
• #### 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