org.jgrapht.alg

## Class FloydWarshallShortestPaths<V,E>

• Type Parameters:
`V` - the graph vertex type
`E` - the graph edge type

```public class FloydWarshallShortestPaths<V,E>
extends Object```
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. Warning: This code has not been tested (and probably doesn't work) on multi-graphs. Code should be updated to work properly on multi-graphs.
Author:
Tom Larkworthy, Soren Davidsen (soren@tanesha.net), Joris Kinable
• ### 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
`double` `getDiameter()`
`V` ```getFirstHop(V a, V b)```
Returns the first hop, i.e., the second node on the shortest path from a to b.
`Graph<V,E>` `getGraph()`
`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>` ```getShortestPath(V a, V b)```
Get the shortest path between two vertices.
`List<V>` ```getShortestPathAsVertexList(V a, V b)```
Get the shortest path between two vertices as a list of vertices.
`List<GraphPath<V,E>>` `getShortestPaths()`
Get all shortest paths in the graph.
`List<GraphPath<V,E>>` `getShortestPaths(V v)`
Get shortest paths from a vertex to all other vertices in the graph.
`int` `getShortestPathsCount()`
`double` ```shortestDistance(V a, V b)```
Get the length of a shortest path.
• ### Methods inherited from class java.lang.Object

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

• #### getGraph

`public Graph<V,E> getGraph()`
Returns:
the graph on which this algorithm operates
• #### getShortestPathsCount

`public int getShortestPathsCount()`
Returns:
total number of shortest paths
• #### shortestDistance

```public double shortestDistance(V a,
V b)```
Get the length of a shortest path.
Parameters:
`a` - first vertex
`b` - second vertex
Returns:
shortest distance between a and b
• #### getDiameter

`public double getDiameter()`
Returns:
the diameter (longest of all the shortest paths) computed for the graph. If the graph is vertexless, return 0.0.
• #### getShortestPath

```public GraphPath<V,E> getShortestPath(V a,
V b)```
Get the shortest path between two vertices.
Parameters:
`a` - from vertex
`b` - to vertex
Returns:
the path, or null if none found
• #### getShortestPathAsVertexList

```public List<V> getShortestPathAsVertexList(V a,
V b)```
Get the shortest path between two vertices as a list of vertices.
Parameters:
`a` - from vertex
`b` - to vertex
Returns:
the path, or null if none found
• #### getShortestPaths

`public List<GraphPath<V,E>> getShortestPaths(V v)`
Get shortest paths from a vertex to all other vertices in the graph.
Parameters:
`v` - the originating vertex
Returns:
List of paths
• #### getShortestPaths

`public List<GraphPath<V,E>> getShortestPaths()`
Get all shortest paths in the graph.
Returns:
List of 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 getShortestPathAsVertexList(a,b).get(0);
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 getShortestPathAsVertexList(a,b).get(shortestPathListSize-1);. 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.