## mark a section (Learn more)

# Justin Ethier # Solution to ruby quiz 157 class Point < Struct.new(:x, :y) def self.random Point.new(rand, rand) end def to_s "(#{x}, #{y})" end end class Circle < Struct.new(:center, :radius) def to_s "{center:#{center}, radius:#{radius}}" end end # Calculate distance between points def distance(pt_a, pt_b) Math.sqrt((pt_a.x - pt_b.x) * (pt_a.x - pt_b.x) + (pt_a.y - pt_b.y) * (pt_a.y - pt_b.y)) end # Determine if given points are all within a circle def inside_circle?(points, circle) for point in points dist = distance(point, circle.center) return false if dist > circle.radius end true end def encircle(points) # takes array of Point objects # find the average midpoint of all points mid = Point.new( points.inject(0){|sum, pt| sum += pt.x} / (points.size * 1.0), points.inject(0){|sum, pt| sum += pt.y} / (points.size * 1.0)) # sort points by longest distance from midpoint # longest point (index 0) is the initial radius points.sort!{|a,b| distance(mid, a) <=> distance(mid, b) }.reverse! # Taking the average midpoint does not necessarily work because the points may # be weighted more heavily to one side. We correct for this by sliding the circle # along the line from its original center to the outmost point, decreasing the # radius as we go. Keep doing this until the circle can be made no smaller. point = points[0] slope = (mid.y - point.y) / (mid.x - point.x) new_pt, delta, sign = mid, 0.0, 1.0 sign = -1.0 if mid.x > point.x while inside_circle?(points, Circle.new(new_pt, distance(new_pt, point))) mid = new_pt delta += 0.000001 * sign new_pt = Point.new(mid.x + delta, mid.y + (slope * (delta))) end return Circle.new(mid, distance(mid, point)) end def generate_samples(n) (1..n).map { Point.random } end

This paste will be private.