private void PrepareTree()
{
int centerCount = 0;
List <int[]> allCenters = new List <int[]>(forest.NumberOfTrees);
int[] roots = forest.GetRoots();
foreach (int rId in roots)
{
int[] centers = forest.GetCenter(rId);
centerCount += centers.Length;
allCenters.Add(centers);
}
foreach (int[] centers in allCenters)
{
forest.SetToRoot(centers[0]);
}
if (centerCount > 1)
{
// Forest is not connected or has two centers.
// Add dummy root.
isDummyRoot = true;
rootId = forest.AddVertex();
foreach (int[] centers in allCenters)
{
foreach (int c in centers)
{
forest.SetParent(c, rootId);
}
}
}
else
{
isDummyRoot = false;
rootId = allCenters[0][0];
}
}
private void Preprocess()
{
hypertree.TransformToDual();
// Generate and "draw" underlying tree.
joinForest = hypertree.GetJoinTree();
drawer = new RootedDrawing(joinForest);
data = drawer.DrawRadial();
// Computes colouring and max colour.
colouring = hypertree.GetVertexColouring();
hypertree.TransformToDual();
maxCol = 0;
for (int i = 0; i < colouring.Length; i++)
{
maxCol = Math.Max(colouring[i], maxCol);
}
// Counting sort to sort edges by their colour.
edgeByColour = new int[colouring.Length];
int[] colCounter = new int[maxCol + 1];
for (int i = 0; i < colouring.Length; i++)
{
colCounter[colouring[i]]++;
}
for (int i = 1; i < colCounter.Length; i++)
{
colCounter[i] += colCounter[i - 1];
}
for (int i = colouring.Length - 1; i >= 0; i--)
{
int col = colouring[i];
colCounter[col]--;
int ind = colCounter[col];
edgeByColour[ind] = i;
}
// End of counting sort.
Array.Reverse(edgeByColour);
edges = new List <int> [hypertree.NoOfEdges];
for (int i = 0; i < edges.Length; i++)
{
edges[i] = new List <int>(Math.Max(hypertree.GetCardinality(i) * 2 - 2, 0));
}
// Use a DFS to determine the tree-edges of each hyperedge.
// The search starts at the root.
// Each time the search reaces a vertex v, it checks for all edges e containing v, if e is already activated.
// If e is already activated, the tree-edge from v to its parent is part of the edge.
bool[] activeEdges = new bool[hypertree.NoOfEdges];
Stack <int> verStack = new Stack <int>();
Stack <int> parStack = new Stack <int>();
int[] rootIds = joinForest.GetRoots();
foreach (int rId in rootIds)
{
verStack.Push(rId);
parStack.Push(-1);
while (verStack.Count > 0)
{
int vId = verStack.Pop();
int pId = parStack.Pop();
int[] edgeIds = hypertree.GetEdges(vId);
foreach (int eId in edgeIds)
{
if (activeEdges[eId])
{
edges[eId].Add(pId);
edges[eId].Add(vId);
}
activeEdges[eId] = true;
}
int[] neighs = joinForest[vId];
foreach (int nId in neighs)
{
if (nId == pId)
{
continue;
}
verStack.Push(nId);
parStack.Push(vId);
}
}
}
// Now, data contains the radial coordinates of each vertex,
// edges contains the list of tree-edges of each hyperedge,
// colouring contains the colours of each hyperedge,
// and edgeByColur has the edges ordered by their colour.
}
