/// <summary>
/// Creates balanced tree from a sorted list.
/// </summary>
/// <param name="rangeTreePoints">Points to store in the tree</param>
/// <returns>New (Y) range tree.</returns>
private RangeTreeNode <TValue> CreateBalancedTree(List <ValueTuple <TValue, TValue> > rangeTreePoints)
{
if (rangeTreePoints.Count == 0)
{
return(null);
}
var medVal = rangeTreePoints[rangeTreePoints.Count / 2];
var median = new RangeTreeNode <TValue>(medVal, Alpha, 1);
if (rangeTreePoints.Count == 1)
{
return(median);
}
rangeTreePoints.Remove(medVal);
var midsons = FindMiddleSons(rangeTreePoints, medVal, 1);
median.SetMiddleSons(midsons);
var smallerInY = GetSmallerThanPoint(rangeTreePoints, medVal, yComparer);
// build sons
median.SetLeftSon(CreateBalancedTree(smallerInY));
median.SetRightSon(CreateBalancedTree(rangeTreePoints));
return(median);
}
/// <summary>
/// Main build method, build a tree from a list of points, given that the nodes are sorted by last coordinate.
/// </summary>
/// <param name="rangeTreePoints">Points to store in new range tree. </param>
/// <param name="sortingCoordinate">Sorting coordinate of new tree.</param>
/// <returns>New balanced range tree.</returns>
private RangeTreeNode <TValue> Build(List <ValueTuple <TValue, TValue> > rangeTreePoints, int sortingCoordinate)
{
if (rangeTreePoints.Count == 0)
{
return(null);
}
if (rangeTreePoints.Count == 1)
{
var node = new RangeTreeNode <TValue>(rangeTreePoints[0], Alpha, sortingCoordinate);
return(node);
}
if (sortingCoordinate == 1)
{
// another y tree
lastOpVisitedNodes += rangeTreePoints.Count;
return(CreateBalancedTree(rangeTreePoints));
}
// find median, build its other dimension tree
var medVal = rangeTreePoints.Median(xComparer);
var median = new RangeTreeNode <TValue>(medVal, Alpha, 0);
median.OtherDimensionSubtree = new RangeTree <TValue>(Build(new List <(TValue, TValue)>(rangeTreePoints), sortingCoordinate + 1), Alpha);
// find nodes with same x-value, set is as middle nodes
rangeTreePoints.Remove(medVal);
var midsons = FindMiddleSons(rangeTreePoints, medVal, sortingCoordinate);
median.SetMiddleSons(midsons);
// split nodes by x-value of median
var smallerInX = GetSmallerThanPoint(rangeTreePoints, medVal, xComparer);
// build sons
median.SetLeftSon(Build(smallerInX, sortingCoordinate));
median.SetRightSon(Build(rangeTreePoints, sortingCoordinate));
return(median);
}
