new tasks

Task/Closest-pair_problem/Ruby/closest_pair_problem.rb

@@ -0,0 +1,68 @@
+Point = Struct.new(:x, :y)
+
+def distance(p1, p2)
+  Math.hypot(p1.x - p2.x, p1.y - p2.y)
+end
+
+def closest_bruteforce(points)
+  mindist, minpts = Float::MAX, []
+  points.length.times do |i|
+    (i+1).upto(points.length - 1) do |j|
+      dist = distance(points[i], points[j])
+      if dist < mindist
+        mindist = dist
+        minpts = [points[i], points[j]]
+      end
+    end
+  end
+  [mindist, minpts]
+end
+
+def closest_recursive(points)
+  if points.length <= 3
+    return closest_bruteforce(points)
+  end
+  xP = points.sort_by {|p| p.x}
+  mid = (points.length / 2.0).ceil
+  pL = xP[0,mid]
+  pR = xP[mid..-1]
+  dL, pairL = closest_recursive(pL)
+  dR, pairR = closest_recursive(pR)
+  if dL < dR
+    dmin, dpair = dL, pairL
+  else
+    dmin, dpair = dR, pairR
+  end
+  yP = xP.find_all {|p| (pL[-1].x - p.x).abs < dmin}.sort_by {|p| p.y}
+  closest = Float::MAX
+  closestPair = []
+  0.upto(yP.length - 2) do |i|
+    (i+1).upto(yP.length - 1) do |k|
+      break if (yP[k].y - yP[i].y) >= dmin
+      dist = distance(yP[i], yP[k])
+      if dist < closest
+        closest = dist
+        closestPair = [yP[i], yP[k]]
+      end
+    end
+  end
+  if closest < dmin
+    [closest, closestPair]
+  else
+    [dmin, dpair]
+  end
+end
+
+
+points = Array.new(100) {Point.new(rand, rand)}
+p ans1 = closest_bruteforce(points)
+p ans2 = closest_recursive(points)
+fail "bogus!" if ans1[0] != ans2[0]
+
+require 'benchmark'
+
+points = Array.new(10000) {Point.new(rand, rand)}
+Benchmark.bm(12) do |x|
+  x.report("bruteforce") {ans1 = closest_bruteforce(points)}
+  x.report("recursive")  {ans2 = closest_recursive(points)}
+end