Package org.jgrapht.alg.shortestpath
Class FloydWarshallShortestPaths<V,E>
- java.lang.Object
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- org.jgrapht.alg.shortestpath.FloydWarshallShortestPaths<V,E>
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- Type Parameters:
V
- the graph vertex typeE
- the graph edge type
- All Implemented Interfaces:
ShortestPathAlgorithm<V,E>
public class FloydWarshallShortestPaths<V,E> extends java.lang.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
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Nested Class Summary
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Nested classes/interfaces inherited from interface org.jgrapht.alg.interfaces.ShortestPathAlgorithm
ShortestPathAlgorithm.SingleSourcePaths<V,E>
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Field Summary
Fields Modifier and Type Field Description protected Graph<V,E>
graph
The underlying graph.protected static java.lang.String
GRAPH_CONTAINS_A_NEGATIVE_WEIGHT_CYCLE
Error message for reporting the existence of a negative-weight cycle.protected static java.lang.String
GRAPH_MUST_CONTAIN_THE_SINK_VERTEX
Error message for reporting that a sink vertex is missing.protected static java.lang.String
GRAPH_MUST_CONTAIN_THE_SOURCE_VERTEX
Error message for reporting that a source vertex is missing.
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Constructor Summary
Constructors Constructor Description FloydWarshallShortestPaths(Graph<V,E> graph)
Create a new instance of the Floyd-Warshall all-pairs shortest path algorithm.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method 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.
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Field Detail
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GRAPH_CONTAINS_A_NEGATIVE_WEIGHT_CYCLE
protected static final java.lang.String GRAPH_CONTAINS_A_NEGATIVE_WEIGHT_CYCLE
Error message for reporting the existence of a negative-weight cycle.- See Also:
- Constant Field Values
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GRAPH_MUST_CONTAIN_THE_SOURCE_VERTEX
protected static final java.lang.String GRAPH_MUST_CONTAIN_THE_SOURCE_VERTEX
Error message for reporting that a source vertex is missing.- See Also:
- Constant Field Values
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GRAPH_MUST_CONTAIN_THE_SINK_VERTEX
protected static final java.lang.String GRAPH_MUST_CONTAIN_THE_SINK_VERTEX
Error message for reporting that a sink vertex is missing.- See Also:
- Constant Field Values
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graph
protected final Graph<V,E> graph
The underlying graph.
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Method Detail
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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
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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 vertexb
- the target vertex- Returns:
- a shortest path or null if no path exists
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getPathWeight
public double getPathWeight(V source, V sink)
Get the weight of the shortest path from a source vertex to a sink vertex. ReturnsDouble.POSITIVE_INFINITY
if no path exists.- Specified by:
getPathWeight
in interfaceShortestPathAlgorithm<V,E>
- Parameters:
source
- the source vertexsink
- 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
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getPaths
public ShortestPathAlgorithm.SingleSourcePaths<V,E> getPaths(V source)
Compute all shortest paths starting from a single source vertex.- Specified by:
getPaths
in interfaceShortestPathAlgorithm<V,E>
- Parameters:
source
- the source vertex- Returns:
- the shortest paths
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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 callinggetPath(Object, Object)
and then reading the first vertex.- Parameters:
a
- source vertexb
- target vertex- Returns:
- next hop on the shortest path from a to b, or null when there exists no path from $a$ to $b$.
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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 callinggetPath(Object, Object)
and then reading the vertex. The first invocation of this method populates a last hop matrix.- Parameters:
a
- source vertexb
- target vertex- Returns:
- last hop on the shortest path from $a$ to $b$, or null when there exists no path from $a$ to $b$.
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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 vertexsink
- the sink vertex- Returns:
- an empty path or null null if the source vertex is different than the target vertex
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