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 List <GraphVertex> FindShortestPath(
string startVertexUniqueKey,
string targetVertexUniqueKey)
{
GraphVertex startVertex = weightedGraph.GetVertexByUniqueKey(startVertexUniqueKey);
GraphVertex targetVertex = weightedGraph.GetVertexByUniqueKey(targetVertexUniqueKey);
// initialize the 'prev' data structure that will hold the path
Dictionary <string, GraphVertex> prev = new Dictionary <string, GraphVertex>();
// initialize the priority queue
PriorityQueue remainingVertices = new KevinPriorityQueue();
foreach (GraphVertex v in weightedGraph.GetAllVertices())
{
int totalPathWeightThroughCurrentVertex = v.UniqueKey == startVertex.UniqueKey ?
0 :
int.MaxValue;
remainingVertices.Enqueue(
new ShortestPathPriorityQueueNode(data: v, priority: totalPathWeightThroughCurrentVertex));
}
while (remainingVertices.Count() > 0)
{
PriorityQueueNode currentNode = remainingVertices.Dequeue();
GraphVertex currentVertex = currentNode.Data as GraphVertex;
foreach (GraphEdge edge in currentVertex.GetIncidentEdges())
{
GraphVertex edgeTarget = weightedGraph.GetVertexByUniqueKey(edge.TargetVertexUniqueKey);
if (!remainingVertices.Contains(edgeTarget.UniqueKey))
{
continue;
}
int newDist = currentNode.Priority + edge.Weight;
PriorityQueueNode targetNode = remainingVertices.Peek(edgeTarget.UniqueKey);
if (newDist < targetNode.Priority)
{
remainingVertices.ChangePriority(targetNode.Data.UniqueKey, newDist);
prev[edgeTarget.UniqueKey] = currentVertex;
}
}
if (currentVertex.UniqueKey == targetVertex.UniqueKey)
{
break;
}
}
return(BuildPath(prev, startVertexUniqueKey, targetVertexUniqueKey));
}