/// <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>
/// <param name="edges">Cache for the edges used.</param>
public void Span(int startIndex, ITwoDArray <DirectedGraphEdge> edges)
{
// 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(edges[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(edges[newIn, otherNode]);
}
}
}
}
SpanningEdges = mstEdges;
}
/// <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>
/// <param name="edges">Cache for the edges used.</param>
public void Span(int startIndex, ITwoDArray<DirectedGraphEdge> edges)
{
// 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(edges[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(edges[newIn, otherNode]);
}
}
}
}
SpanningEdges = mstEdges;
}
public override void Initialize()
{
base.Initialize();
OnFinalSearchSpaceCreated();
var totalCount = SearchSpace.Count + TargetNodes.Count;
// Create edges
var edges = new DirectedGraphEdge[totalCount, totalCount];
for (int i = 0; i < totalCount; i++)
{
for (int j = 0; j < totalCount; j++)
{
edges[i, j] = new DirectedGraphEdge(i, j, Distances[i, j]);
}
}
_edges = new TwoDArray <DirectedGraphEdge>(edges);
// Sort edges if PreFilledSpanThreshold is satisfied.
if (TargetNodes.Count / (double)totalCount >= PreFilledSpanThreshold)
{
using (var prioQueue = new LinkedListPriorityQueue <DirectedGraphEdge>(100, totalCount * totalCount))
{
// A PriorityQueue is used for sorting. Should be faster than sorting-methods that don't exploit
// sorting ints.
var enqueued = 0;
for (var i = 0; i < totalCount; i++)
{
for (var j = i + 1; j < totalCount; j++)
{
prioQueue.Enqueue(_edges[i, j]);
enqueued++;
}
}
_orderedEdges = new List <DirectedGraphEdge>(enqueued);
while (!prioQueue.IsEmpty)
{
_orderedEdges.Add(prioQueue.Dequeue());
}
}
}
InitializeGa();
}
