org.protempa.graph

Class BellmanFord

java.lang.Object

org.protempa.graph.BellmanFord

public final class BellmanFord
extends Object

An implementation of the Bellman-Ford single-source shortest paths algorithm. The implementation can look for the shortest paths from a source or to a destination. It runs in O(n^2) time, where n is the number of vertices in the graph.

Author:

Andrew Post

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	BellmanFord.Mode For setting whether the Bellman-Ford algorithm should look for the shortest paths from a source or to a destination.

Method Summary

Modifier and Type	Method and Description
static Map<?,Weight>	calcShortestDistances(Object sourceOrDest, DirectedGraph g, BellmanFord.Mode mode) Calculates the distance of every object in a graph from a source object.
static boolean	hasNegativeCycle(Object sourceOrDest, DirectedGraph g, BellmanFord.Mode mode) Determines if there are any negative cycles found.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

calcShortestDistances

public static Map<?,Weight> calcShortestDistances(Object sourceOrDest,
                                                  DirectedGraph g,
                                                  BellmanFord.Mode mode)

Calculates the distance of every object in a graph from a source object. It calls hasNegativeCycles(), and if no negative cycles are found, returns the shortest distances.

Parameters:

sourceOrDest - a vertex.

Returns:

a newly created Map of objects and their distances from the source object, or null if a negative cycle was encountered.

hasNegativeCycle

public static boolean hasNegativeCycle(Object sourceOrDest,
                                       DirectedGraph g,
                                       BellmanFord.Mode mode)

Determines if there are any negative cycles found.

Parameters:

sourceOrDest - a vertex.

Returns:

true if a negative cycle was found, false otherwise.