/// <summary>
/// Uses Prim's algorithm to build an MST spanning the mstNodes.
/// O(|mstNodes|^2) runtime.
/// </summary>
/// <param name="startFrom">A GraphNode to start from.</param>
public void Span(GraphNode startFrom)
{
var adjacentEdgeQueue = new LinkedListPriorityQueue <LinkedGraphEdge>(100);
var startIndex = startFrom.DistancesIndex;
// All nodes that are not yet included.
var toAdd = new List <int>(_mstNodes.Count);
// If the index node is already included.
var inMst = new bool[_distances.CacheSize];
// The spanning edges.
var mstEdges = new List <GraphEdge>(_mstNodes.Count);
for (var i = 0; i < _mstNodes.Count; i++)
{
var index = _mstNodes[i].DistancesIndex;
if (index != startIndex)
{
toAdd.Add(index);
var adjacentEdge = new LinkedGraphEdge(startIndex, index);
adjacentEdgeQueue.Enqueue(adjacentEdge, _distances[startIndex, index]);
}
}
inMst[startIndex] = true;
while (toAdd.Count > 0 && adjacentEdgeQueue.Count > 0)
{
int newIn;
LinkedGraphEdge shortestEdge;
// Dequeue and ignore edges that are already inside the MST.
// Add the first one that is not.
do
{
shortestEdge = adjacentEdgeQueue.Dequeue();
newIn = shortestEdge.Outside;
} while (inMst[newIn]);
mstEdges.Add(new GraphEdge(
_distances.IndexToNode(shortestEdge.Inside),
_distances.IndexToNode(shortestEdge.Outside)));
inMst[newIn] = true;
// Find all newly adjacent edges and enqueue them.
for (var i = 0; i < toAdd.Count; i++)
{
var otherNode = toAdd[i];
if (otherNode == newIn)
{
toAdd.RemoveAt(i--);
}
else
{
var edge = new LinkedGraphEdge(newIn, otherNode);
adjacentEdgeQueue.Enqueue(edge, _distances[newIn, otherNode]);
}
}
}
SpanningEdges = mstEdges;
IsSpanned = true;
}
/// <summary>
/// Uses Prim's algorithm to build an MST spanning the mstNodes.
/// O(|mstNodes|^2) runtime.
/// </summary>
/// <param name="startIndex">The node index to start from.</param>
public void Span(int startIndex)
{
// All nodes that are not yet included.
var toAdd = new List <int>(_mstNodes.Count);
// If the index node is already included.
var inMst = new bool[_distances.CacheSize];
// The spanning edges.
var mstEdges = new List <DirectedGraphEdge>(_mstNodes.Count);
using (var adjacentEdgeQueue = new LinkedListPriorityQueue <DirectedGraphEdge>(100, _mstNodes.Count * _mstNodes.Count))
{
foreach (var t in _mstNodes)
{
if (t != startIndex)
{
toAdd.Add(t);
adjacentEdgeQueue.Enqueue(new DirectedGraphEdge(startIndex, t),
_distances[startIndex, t]);
}
}
inMst[startIndex] = true;
while (toAdd.Count > 0 && !adjacentEdgeQueue.IsEmpty)
{
int newIn;
DirectedGraphEdge shortestEdge;
// Dequeue and ignore edges that are already inside the MST.
// Add the first one that is not.
do
{
shortestEdge = adjacentEdgeQueue.Dequeue();
newIn = shortestEdge.Outside;
} while (inMst[newIn]);
mstEdges.Add(shortestEdge);
inMst[newIn] = true;
// Find all newly adjacent edges and enqueue them.
for (var i = 0; i < toAdd.Count; i++)
{
var otherNode = toAdd[i];
if (otherNode == newIn)
{
toAdd.RemoveAt(i--);
}
else
{
adjacentEdgeQueue.Enqueue(new DirectedGraphEdge(newIn, otherNode),
_distances[newIn, otherNode]);
}
}
}
}
SpanningEdges = mstEdges;
}
