public static List <Edge <T> > GetMSTUsingPrims <T>(this Graph <T> g)
{
BinaryMinHeap <Vertex <T> > minHeap = new BinaryMinHeap <Vertex <T> >();
//Set all nodes in hash map to infinity
Dictionary <Vertex <T>, Edge <T> > vertexToEdgeMap = new Dictionary <Vertex <T>, Edge <T> >();
//Final result
var result = new List <Edge <T> >();
//insert all vertices with infinite value initially.
foreach (var v in g.AllVertex.Values)
{
minHeap.AddNode(Int32.MaxValue, v);
}
//Start from Random Vertex and decrease min heap to 0
Vertex <T> startVertex = g.AllVertex.FirstOrDefault().Value;
minHeap.Decrease(startVertex, 0);
//iterate till heap + map has elements in it
while (!minHeap.IsEmpty())
{
//Extract the min vertex from heap
var minVertex = minHeap.extractMin().Data;
//get the corresponding edge for this vertex if present and add it to final result.
//This edge wont be present for first vertex.
Edge <T> spanningTreeEdge = vertexToEdgeMap.ContainsKey(minVertex) ? vertexToEdgeMap[minVertex] : null;
if (spanningTreeEdge != null)
{
result.Add(spanningTreeEdge);
}
//Iterate through all the edges for the current minVertex
foreach (var edge in minVertex.GetAdjEdges())
{
Vertex <T> otherVertex = GetVertexForEdge(minVertex, edge);
//Check if the other vertex already exists in the map and weight attached is greater than weight of the edge. If yes, replace
if (minHeap.ContainsData(otherVertex) && minHeap.GetWeight(otherVertex) > edge.Weight)
{
minHeap.Decrease(otherVertex, edge.Weight);
if (vertexToEdgeMap.ContainsKey(otherVertex))
{
vertexToEdgeMap[otherVertex] = edge;
}
else
{
vertexToEdgeMap.Add(otherVertex, edge);
}
}
}
}
return(result);
}
private static void TestBinaryMinHeap()
{
BinaryMinHeap <String> heap = new BinaryMinHeap <String>();
heap.AddNode(3, "Tushar");
heap.AddNode(4, "Ani");
heap.AddNode(8, "Vijay");
heap.AddNode(10, "Pramila");
heap.AddNode(5, "Roy");
heap.AddNode(6, "NTF");
heap.PrintHeap();
heap.Decrease("Pramila", 1);
heap.Decrease("Vijay", 1);
heap.Decrease("Ani", 11);
heap.Decrease("NTF", 4);
heap.PrintHeap();
var node = heap.extractMin();
while (node != null)
{
Console.WriteLine("Min Node extracted is :" + node.Data + " " + node.Weight);
heap.PrintHeap();
node = heap.extractMin();
}
}
public static Dictionary <Vertex <T>, Int32> DjkstrasAlgo <T>(this Graph <T> g, Vertex <T> source, Dictionary <Vertex <T>, Vertex <T> > pathMap)
{
BinaryMinHeap <Vertex <T> > minHeap = new BinaryMinHeap <Vertex <T> >();
Dictionary <Vertex <T>, Int32> distanceMap = new Dictionary <Vertex <T>, int>();
//Dictionary<Vertex<T>, Vertex<T>> pathMap = new Dictionary<Vertex<T>, Vertex<T>>();
//Set all weights to infinity in minHeap
foreach (var v in g.AllVertex.Values)
{
minHeap.AddNode(Int32.MaxValue, v);
}
//Decrease the weight of source to 0
minHeap.Decrease(source, 0);
pathMap.Add(source, null);
while (!minHeap.IsEmpty())
{
//Extract the min
int weight = minHeap.MinNode().Weight;
var currentVertex = minHeap.extractMin().Data;
distanceMap.AddOrUpdateDictionary(currentVertex, weight);
foreach (var edge in currentVertex.GetAdjEdges())
{
var otherVertex = GetVertexForEdge(currentVertex, edge);
if (minHeap.ContainsData(otherVertex) && minHeap.GetWeight(otherVertex) > (edge.Weight + weight))
{
minHeap.Decrease(otherVertex, (edge.Weight + weight));
pathMap.AddOrUpdateDictionary(otherVertex, currentVertex);
}
}
}
return(distanceMap);
}