public void CopyInto(T[] vals, int i)
{
CDLL <T> node = this;
do
{
vals[i++] = node.val; // still, implicit checkcasts at runtime
node = node.next;
} while (node != this);
}
public void PrintFwd()
{
CDLL <T> node = this;
do
{
Console.WriteLine(node.val);
node = node.next;
} while (node != this);
Console.WriteLine();
}
public int Size()
{
int count = 0;
CDLL <T> node = this;
do
{
count++;
node = node.next;
} while (node != this);
return(count);
}
public static Point[] ConvexHull(Point[] pts)
{
// Sort points lexicographically by increasing (x, y)
int N = pts.Length;
Polysort.Quicksort <Point>(pts);
Point left = pts[0], right = pts[N - 1];
// Partition into lower hull and upper hull
CDLL <Point> lower = new CDLL <Point>(left), upper = new CDLL <Point>(left);
for (int i = 0; i < N; i++)
{
double det = Point.Area2(left, right, pts[i]);
if (det > 0)
{
upper = upper.Append(new CDLL <Point>(pts[i]));
}
else if (det < 0)
{
lower = lower.Prepend(new CDLL <Point>(pts[i]));
}
}
lower = lower.Prepend(new CDLL <Point>(right));
upper = upper.Append(new CDLL <Point>(right)).Next;
// Eliminate points not on the hull
eliminate(lower);
eliminate(upper);
// Eliminate duplicate endpoints
if (lower.Prev.val.Equals(upper.val))
{
lower.Prev.Delete();
}
if (upper.Prev.val.Equals(lower.val))
{
upper.Prev.Delete();
}
// Join the lower and upper hull
Point[] res = new Point[lower.Size() + upper.Size()];
lower.CopyInto(res, 0);
upper.CopyInto(res, lower.Size());
return(res);
}
// Graham's scan
private static void eliminate(CDLL <Point> start)
{
CDLL <Point> v = start, w = start.Prev;
bool fwd = false;
while (v.Next != start || !fwd)
{
if (v.Next == w)
{
fwd = true;
}
if (Point.Area2(v.val, v.Next.val, v.Next.Next.val) < 0) // right turn
{
v = v.Next;
}
else
{ // left turn or straight
v.Next.Delete();
v = v.Prev;
}
}
}
public CDLL <T> Append(CDLL <T> elt)
{
elt.prev = this; elt.next = next; next.prev = elt; next = elt;
return(elt);
}
public CDLL <T> Prepend(CDLL <T> elt)
{
elt.next = this; elt.prev = prev; prev.next = elt; prev = elt;
return(elt);
}
// Delete: adjust the remaining elements, make this one point nowhere
public void Delete()
{
next.prev = prev; prev.next = next;
next = prev = null;
}
// A new CDLL node is a one-element circular list
public CDLL(T val)
{
this.val = val; next = prev = this;
}