public static IEnumerable <Tuple <TVertex, TVertex> > GetMST(UndirectedWeightedGraph <TVertex> graph)
{
if (graph == null)
{
throw new ArgumentNullException("graph", "Specify a non-null argument.");
}
if (graph.VertexCount == 0)
{
yield break;
}
if (ConnectedComponents <TVertex> .GetConnectedComponentsCount(graph) > 1)
{
throw new ArgumentException("Graph is not connected.");
}
TVertex source = graph.GetVertices().First();
PriorityQueue <QueueItem> queue = new PriorityQueue <QueueItem>();
Dictionary <TVertex, QueueItem> notSpanned = new Dictionary <TVertex, QueueItem>();
foreach (TVertex vertex in graph.GetVertices().Where(v => !v.Equals(source)))
{
double costToSpan = graph.GetEdgeWeight(source, vertex);
TVertex src = costToSpan < double.PositiveInfinity ? source : default(TVertex);
QueueItem item = new QueueItem(vertex, src, costToSpan);
notSpanned.Add(vertex, item);
queue.Enqueue(item);
}
List <Tuple <TVertex, TVertex> > mst = new List <Tuple <TVertex, TVertex> >();
while (!queue.IsEmpty())
{
QueueItem toSpan = queue.Dequeue();
yield return(Tuple.Create(toSpan.Source, toSpan.VertexToSpan));
notSpanned.Remove(toSpan.VertexToSpan);
foreach (TVertex vertex in graph.GetNeighbours(toSpan.VertexToSpan).Where(v => notSpanned.ContainsKey(v)))
{
QueueItem toRelax = queue.Dequeue(notSpanned[vertex]);
double costToSpan = graph.GetEdgeWeight(toSpan.VertexToSpan, vertex);
if (costToSpan < toRelax.CostToSpan)
{
toRelax.CostToSpan = costToSpan;
toRelax.Source = toSpan.VertexToSpan;
}
queue.Enqueue(toRelax);
}
}
}
public static IEnumerable <Tuple <TVertex, TVertex> > GetMST(UndirectedWeightedGraph <TVertex> graph)
{
if (graph == null)
{
throw new ArgumentNullException("graph", "Specify a non-null argument.");
}
if (graph.VertexCount == 0)
{
yield break;
}
if (ConnectedComponents <TVertex> .GetConnectedComponentsCount(graph) > 1)
{
throw new InvalidOperationException("Graph is not connected.");
}
PriorityQueue <Edge> queue = new PriorityQueue <Edge>();
UnionFind <TVertex> connectedComponents = new UnionFind <TVertex>();
foreach (TVertex vertex in graph.GetVertices())
{
connectedComponents.Add(vertex);
foreach (TVertex neighbour in graph.GetNeighbours(vertex))
{
queue.Enqueue(new Edge(vertex, neighbour, graph.GetEdgeWeight(vertex, neighbour)));
}
}
List <Tuple <TVertex, TVertex> > mst = new List <Tuple <TVertex, TVertex> >();
while (!queue.IsEmpty())
{
Edge minCostEdge = queue.Dequeue();
if (!connectedComponents.AreConnected(minCostEdge.Vertex1, minCostEdge.Vertex2))
{
yield return(Tuple.Create(minCostEdge.Vertex1, minCostEdge.Vertex2));
connectedComponents.Union(minCostEdge.Vertex1, minCostEdge.Vertex2);
}
}
}
