Created
February 10, 2014 13:59
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| import scala.collection.mutable.ListBuffer | |
| case class Point(x: Double, y: Double) | |
| /** Compute the convex hull of given points. Returns vertices ordered ccw */ | |
| def convexHull(_points: Seq[Point]): Seq[Point] = { | |
| val points = _points.sortBy(_.x) | |
| val upper = halfHull(points) | |
| val lower = halfHull(points.reverse) | |
| upper.remove(0) | |
| lower.remove(0) | |
| upper ++: lower | |
| } | |
| def halfHull(points: Seq[Point]) = { | |
| val upper = new ListBuffer[Point]() | |
| for (p <- points) { | |
| while (upper.size >= 2 && leftTurn(p, upper(0), upper(1))) { | |
| upper.remove(0) | |
| } | |
| upper.prepend(p) | |
| } | |
| upper | |
| } | |
| def leftTurn(p1: Point, p2: Point, p3: Point) = { | |
| val slope = (p2.x - p1.x) * (p3.y - p1.y) - (p2.y - p1.y) * (p3.x - p1.x) | |
| val collinear = math.abs(slope) <= 1e-9 | |
| val leftTurn = slope < 0 | |
| collinear || leftTurn | |
| } |
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