SweepClosestPair.cs

public static Tuple<Point, Point> FindClosestPoints(List<Point> points, out double minDistance)
        {
            var minDist = double.PositiveInfinity;
            int lastDeleted = 0;
            Point a = new Point();
            Point b = new Point();
            SortedSet<Point> tree = new SortedSet<Point>(new ByY());
            var pointsArray = points.ToArray();
            Array.Sort(pointsArray, new ByX());

            for (int i = 0; i < points.Count; i++)
            {
                var p = pointsArray[i];
                for (int j = lastDeleted; j < i; j++)
                {
                    var q = pointsArray[j];
                    if (p.x - q.x > minDist)
                    {
                        lastDeleted = j;
                        tree.Remove(q);
                    }
                }
                var result = tree.GetViewBetween(new Point(p.x, p.y - minDist), new Point(p.x, p.y + minDist));
                foreach (var q in result)
                {
                    if (Point.Distance(p, q) < minDist)
                    {
                        a = p;
                        b = q;
                        minDist = Point.Distance(p, q);
                    }
                }
                tree.Add(p);
            }

            minDistance = minDist;
            return new Tuple<Point, Point>(a, b);
        }