/// <summary>
/// The Graham Scan algorithm determines the points belonging to the convex hull in O(n lg n).
/// </summary>
/// <param name="points">set of points</param>
/// <returns>points in the convex hull</returns>
/// <seealso href="http://en.wikipedia.org/wiki/Graham_scan">Graham scan, Wikipedia</seealso>
public static List <Point> GrahamScan(List <Point> points)
{
if (points.Count <= 3)
{
return(new List <Point>(points));
}
var ps = new List <Point>(points);
ps.Sort(new CompareYThenX());
ps.Sort(new PolarComparator(ps[0]));
Deque <Point> hull = new ArrayDeque <Point>();
hull.Push(ps[0]);
hull.Push(ps[1]);
hull.Push(ps[2]);
for (int i = 3; i < points.Count; i++)
{
var top = hull.Pop();
while (hull.Any() && !IsLeftTurn(hull.Peek(), top, ps[i]))
{
top = hull.Pop();
}
hull.Push(top);
hull.Push(ps[i]);
}
return(new List <Point>(hull));
}
/// <summary>
/// Visits the given file, returning the {@code Event} corresponding to that
/// visit.
///
/// The {@code ignoreSecurityException} parameter determines whether
/// any SecurityException should be ignored or not. If a SecurityException
/// is thrown, and is ignored, then this method returns {@code null} to
/// mean that there is no event corresponding to a visit to the file.
///
/// The {@code canUseCached} parameter determines whether cached attributes
/// for the file can be used or not.
/// </summary>
private Event Visit(Path entry, bool ignoreSecurityException, bool canUseCached)
{
// need the file attributes
BasicFileAttributes attrs;
try
{
attrs = GetAttributes(entry, canUseCached);
}
catch (IOException ioe)
{
return(new Event(EventType.ENTRY, entry, ioe));
}
catch (SecurityException se)
{
if (ignoreSecurityException)
{
return(null);
}
throw se;
}
// at maximum depth or file is not a directory
int depth = Stack.Size();
if (depth >= MaxDepth || !attrs.Directory)
{
return(new Event(EventType.ENTRY, entry, attrs));
}
// check for cycles when following links
if (FollowLinks && WouldLoop(entry, attrs.FileKey()))
{
return(new Event(EventType.ENTRY, entry, new FileSystemLoopException(entry.ToString())));
}
// file is a directory, attempt to open it
DirectoryStream <Path> stream = null;
try
{
stream = Files.NewDirectoryStream(entry);
}
catch (IOException ioe)
{
return(new Event(EventType.ENTRY, entry, ioe));
}
catch (SecurityException se)
{
if (ignoreSecurityException)
{
return(null);
}
throw se;
}
// push a directory node to the stack and return an event
Stack.Push(new DirectoryNode(entry, attrs.FileKey(), stream));
return(new Event(EventType.START_DIRECTORY, entry, attrs));
}
