/// <summary>
/// Uses the Round-Robin strategy to create a KdTree of the given dimension for the set of points.
/// </summary>
public KdTree(params Point[] points)
{
if (points == null)
{
throw new ArgumentNullException();
}
if (!points.Any())
{
throw new ArgumentOutOfRangeException();
}
dimension = points.First().Dimension();
if (points.Any(p => p.Dimension() != dimension))
{
throw new ArgumentException();
}
Shuffle(points);
// Partitions the points in the range [low, high] into a subtree defined by the cutting dimension l
Node KdTree(int low, int high, int l)
{
if (high < low)
{
return(null);
}
var byLevel = new Point.ByDimension(l);
QuickSort(points, low, high, byLevel);
var mid = low + (high - low) / 2;
var newL = (l + 1) % dimension;
return(new Node
{
point = points[mid],
left = KdTree(low, mid - 1, newL),
right = KdTree(mid + 1, high, newL)
});
}
root = KdTree(0, points.Length - 1, 0);
}
/// <summary>
/// Remove a point <code>p</code> from the tree.
/// raises <exception cref="System.InvalidOperationException"> if the point does not exist.
/// </summary>
public void Delete(Point p)
{
// Implementation ported from CMU Bioinformatics lecture slides (offered by Carl Kingsford)
if (p == null)
{
throw new ArgumentNullException();
}
if (p.Dimension() != dimension)
{
throw new ArgumentException();
}
// Returns the smallest point wrt to the given dimension d
// in the tree rooted at n (here l is the cutting dimension of n)
Point Min(Node n, int d, int l)
{
if (n == null)
{
return(null);
}
var newL = (l + 1) % dimension;
if (l == d)
{
// If we are on the correct plane then we only need to inspect the left branch
if (n.left == null)
{
return(n.point);
}
else
{
return(Min(n.left, d, newL));
}
}
else
{
// Otherwise we need to take a look at both branches
var leftPt = Min(n.left, d, newL);
var rightPt = Min(n.right, d, newL);
var byDim = new Point.ByDimension(d);
if (leftPt == null && rightPt == null)
{
return(n.point);
}
else if (leftPt == null)
{
return(byDim.Min(n.point, rightPt));
}
else if (rightPt == null)
{
return(byDim.Min(n.point, leftPt));
}
else
{
return(byDim.Min(n.point, leftPt, rightPt));
}
}
}
// Delete q from the tree rooted at n (here l is the cutting dimension of n), and return the new subtree
Node Delete(Point q, Node n, int l)
{
if (n == null)
{
throw new InvalidOperationException(); // Not found (it is OK to throw here)
}
var newL = (l + 1) % dimension;
if (n.point == q)
{
// Found the point
if (n.right != null)
{
// Replace the point with the smallest one in the right branch of n
n.point = Min(n.right, l, newL); // n.b. Cannot be null, by design
n.right = Delete(n.point, n.right, newL);
}
else if (n.left != null)
{
// Only have a left branch, so move its contents to the right
n.point = Min(n.left, l, newL);
n.right = Delete(n.point, n.left, newL);
n.left = null;
}
else
{
n = null;
}
}
else if (q[l] < n.point[l])
{
n.left = Delete(q, n.left, newL);
}
else
{
n.right = Delete(q, n.right, newL);
}
return(n);
}
root = Delete(p, root, 0);
}
