protected override int ExecuteTest()
{
if (NodeStates.FixedTargetNodeCount <= 1 || NodeStates.VariableTargetNodeCount > 0)
{
return(0);
}
var removedNodes = 0;
var mst = new MinimalSpanningTree(NodeStates.FixedTargetNodeIndices.ToList(), DistanceLookup);
mst.Span(StartNodeIndex);
var maxEdgeDistance = mst.SpanningEdges.Max(e => e.Priority);
for (var i = 0; i < SearchSpaceSize; i++)
{
if (NodeStates.IsTarget(i) || NodeStates.IsRemoved(i))
{
continue;
}
// Theoretically, this can be sped up by using Voronoi partitions. The Voronoi base of i is the
// terminal with the smallest distance to i by definition, so only the distance to that terminal
// has to be checked.
if (NodeStates.FixedTargetNodeIndices.All(t => DistanceLookup[i, t] >= maxEdgeDistance))
{
EdgeSet.EdgesOf(i).ForEach(EdgeSet.Remove);
NodeStates.MarkNodeAsRemoved(i);
removedNodes++;
}
}
return(removedNodes);
}
protected override int ExecuteTest()
{
// The test only makes sense with at least 2 terminals.
if (NodeStates.FixedTargetNodeCount <= 1)
{
return(0);
}
var removedNodes = 0;
var untested = new HashSet <int>(NodeStates.FixedTargetNodeIndices);
// For each terminal z with degree of at least 2
while (untested.Any())
{
var z = untested.First();
untested.Remove(z);
var neighbors = EdgeSet.NeighborsOf(z);
if (neighbors.Count < 2)
{
continue;
}
// Determine the shortest and second shortest edge incident to z.
// For the second shortest, only the weight is of interest.
var tuple = ShortestTwoEdgesOf(EdgeSet.EdgesOf(z));
var shortest = tuple.Item1;
var secondShortestWeight = tuple.Item2;
// v is the node which is connected to z via the shortest edge.
var v = shortest.N1 == z ? shortest.N2 : shortest.N1;
// The shortest edge belongs to at least one Steiner minimal tree, if
// secondShortestWeight >= shortest.Weight + distance(v, y) for any terminal y, y != z
var canBeContracted = NodeStates.FixedTargetNodeIndices
.Where(y => z != y)
.Any(y => secondShortestWeight >= shortest.Weight + DistanceLookup[v, y]);
// If such a y exists, we can merge v into z.
if (canBeContracted)
{
// z was changed and can be tested again.
untested.Add(z);
// v no longer exists and as such must not be tested.
untested.Remove(v);
MergeInto(v, z);
removedNodes++;
}
}
return(removedNodes);
}