/// <summary>Bellman-Ford algorithm.</summary>
/// <param name="graph">The directed weighted graph.</param>
/// <param name="source">The source vertex.</param>
/// <returns>Dictionary of distances for vertices.</returns>
/// <exception cref="InvalidOperationException">If graph contains a negative cycle.</exception>
public static Dictionary <Vertex <TVertexId>, double> BellmanFord <TVertexId, TVertexProperty, TEdgeProperty>(
IDirectedGraph <TVertexId, TVertexProperty, TEdgeProperty> graph, Vertex <TVertexId> source)
where TEdgeProperty : IWeighted
{
var distances = new Dictionary <Vertex <TVertexId>, double>(
graph.Vertices.Select(v => KeyValuePair.Create(v, IWeighted.Infinity)))
{
[source] = 0.0
};
for (int i = 0; i < graph.VerticesCount - 1; ++i)
{
foreach (Vertex <TVertexId> vertex in graph.Vertices)
{
foreach (Edge <TVertexId> edge in graph.GetAdjacentEdges(vertex))
{
distances[edge.Destination] = Math.Min(distances[edge.Destination],
distances[vertex] + graph.Properties[edge].Weight);
}
}
}
foreach (Vertex <TVertexId> vertex in graph.Vertices)
{
foreach (Edge <TVertexId> edge in graph.GetAdjacentEdges(vertex))
{
if (distances[vertex] < IWeighted.Infinity &&
distances[vertex] + graph.Properties[edge].Weight < distances[edge.Destination])
{
throw new InvalidOperationException("Graph contains a cycle with negative weight");
}
}
}
return(distances);
}
