public Graph GetTree()
{
// initialize the graph that will hold the MST
Graph mst = new KevinGraph();
// initialize the priority queue that will hold the vertices outside the MST
PriorityQueue remainingVertices = new KevinPriorityQueue();
foreach (GraphVertex v in weightedGraph.GetAllVertices())
{
remainingVertices.Enqueue(new MSTPriorityQueueNode(data: v, priority: int.MaxValue));
}
Dictionary <string, GraphEdge> lowestCostEdgeForVertex = new Dictionary <string, GraphEdge>();
while (remainingVertices.Count() > 0)
{
// Get the vertex with the lowest code to add to the MST
// The first vertex is chosen arbitrarily because all vertices start with max cost.
PriorityQueueNode currentNode = remainingVertices.Dequeue();
GraphVertex currentVertex = currentNode.Data as GraphVertex;
// Add the vertex and its lowest cost edge (if any) to the MST
mst.AddVertex(currentVertex.UniqueKey);
if (lowestCostEdgeForVertex.ContainsKey(currentVertex.UniqueKey))
{
GraphEdge lowestCostEdge = lowestCostEdgeForVertex[currentVertex.UniqueKey];
// TO-DO: why?
mst.AddEdge(lowestCostEdge.SourceVertexUniqueKey, lowestCostEdge.TargetVertexUniqueKey, lowestCostEdge.Weight);
mst.AddEdge(lowestCostEdge.TargetVertexUniqueKey, lowestCostEdge.SourceVertexUniqueKey, lowestCostEdge.Weight);
}
// update the minimum cost for each adjacent vertex, and the associated edge
foreach (GraphEdge edge in currentVertex.GetIncidentEdges())
{
GraphVertex edgeTarget = weightedGraph.GetVertexByUniqueKey(edge.TargetVertexUniqueKey);
if (!remainingVertices.Contains(edgeTarget.UniqueKey))
{
continue;
}
int newCost = edge.Weight;
PriorityQueueNode targetNode = remainingVertices.Peek(edgeTarget.UniqueKey);
if (newCost < targetNode.Priority)
{
remainingVertices.ChangePriority(targetNode.Data.UniqueKey, newCost);
lowestCostEdgeForVertex[edgeTarget.UniqueKey] = edge;
}
}
}
return(mst);
}
public static Graph FromString(string s)
{
Dictionary <string, KevinGraphVertex> nameToVertexMap = new Dictionary <string, KevinGraphVertex>();
KevinGraph g = new KevinGraph();
if (string.IsNullOrEmpty(s))
{
return(g);
}
using (StringReader sr = new StringReader(s))
{
while (true)
{
string currentLine = sr.ReadLine();
if (currentLine == null)
{
break;
}
string[] vertices = currentLine.Split(new char[] { ' ' });
if (vertices.Length == 0)
{
continue;
}
KevinGraphVertex vertex = CreateOrGetVertexByName(g, vertices[0], nameToVertexMap);
if (!g.ContainsVertex(vertex.UniqueKey))
{
g.AddVertex(vertex.UniqueKey);
}
for (int i = 1; i < vertices.Length; i++)
{
GraphEdge edge = ParseEdge(g, vertex, vertices[i], nameToVertexMap);
string targetVertexUniqueKey = edge.TargetVertexUniqueKey;
if (!g.ContainsVertex(targetVertexUniqueKey))
{
g.AddVertex(targetVertexUniqueKey);
}
g.AddEdge(edge.SourceVertexUniqueKey, edge.TargetVertexUniqueKey, edge.Weight);
}
}
return(g);
}
}