public Optional <IEnumerable <WeightedEdge <T> > > FindSpanningTreeEdges(IGraph <T> graph)
{
if (graph == null)
{
throw new ArgumentNullException(nameof(graph));
}
if (graph.Count == 0)
{
return(Optional <IEnumerable <WeightedEdge <T> > > .None());
}
var source = _sourceNodeProvider(graph);
var distances = InitializeDistanceTable(graph, source);
var verticesToProcess = new MinBinaryHeap <DistanceInfo <T> >(DistanceInfo <T> .DistanceComparer);
var processedVertices = new HashSet <T>(graph.Comparer);
var spanningTree = new HashSet <WeightedEdge <T> >(WeightedEdge <T> .NonDirectionalComparer(graph.Comparer));
verticesToProcess.Push(DistanceInfo <T> .Zero(source));
while (verticesToProcess.Count > 0)
{
var currentVertex = verticesToProcess.Pop().Single().PreviousVertex;
var sourceDistance = distances[currentVertex];
processedVertices.Add(currentVertex);
if (graph.Comparer.Equals(source, currentVertex) == false)
{
var edge = new WeightedEdge <T>(sourceDistance.PreviousVertex, currentVertex, sourceDistance.Distance);
if (spanningTree.Contains(edge) == false)
{
spanningTree.Add(edge);
}
}
foreach (var destinationVertex in graph.GetAdjacentVertices(currentVertex))
{
if (processedVertices.Contains(destinationVertex))
{
continue;
}
var step = StepMetadata <T> .ForSpanningTree(currentVertex, destinationVertex, distances);
if (step.FoundShorterDistance())
{
distances[destinationVertex] = step.ToSource();
verticesToProcess.Push(step.ToDestination());
}
}
}
return(spanningTree);
}