ABC191-D

Author: minoki

abc/README.md

@@ -438,3 +438,14 @@
 * [x] D - Hachi
 * [ ] E - Transformable Teacher
 * [ ] F - Silver Woods
+
+## AtCoder Beginner Contest 191
+
+<https://atcoder.jp/contests/abc191>
+
+* [ ] A - Vanishing Pitch
+* [ ] B - Remove It
+* [ ] C - Digital Graffiti
+* [x] D - Circle Lattice Points
+* [ ] E - Come Back Quickly
+* [ ] F - GCD or MIN

abc/abc191-d/Main.hs

@@ -0,0 +1,46 @@
+-- https://github.com/minoki/my-atcoder-solutions
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE BangPatterns #-}
+import Data.Int (Int64)
+import qualified Data.ByteString.Char8 as BS
+import Data.Ratio
+
+main = do
+  [cx,cy,r] <- map (read @Double . BS.unpack) . BS.words <$> BS.getLine
+  let cx4, cy4, r4 :: Int64
+      cx4 = round (cx * 10^4)
+      cy4 = round (cy * 10^4)
+      r4 = round (r * 10^4)
+      isInside x y = (10^4 * x - cx4)^2 + (10^4 * y - cy4)^2 <= r4^2
+      minX = ceiling $ (cx4 - r4) % (10^4)
+      maxX = floor $ (cx4 + r4) % (10^4)
+      go1 !acc !x !yB !yT | x > maxX = acc
+                          | otherwise = let yB' = if isInside x yB then
+                                                    let go !y | isInside x (y - 1) = go (y - 1)
+                                                              | otherwise = y
+                                                    in go yB
+                                                  else
+                                                    let go !y | isInside x (y + 1) = y + 1
+                                                              | y > yT = y
+                                                              | otherwise = go (y + 1)
+                                                    in go yB
+                                            yT' = if isInside x yT then
+                                                    let go !y | isInside x (y + 1) = go (y + 1)
+                                                              | otherwise = y
+                                                    in go yT
+                                                  else
+                                                    let go !y | isInside x (y - 1) = y - 1
+                                                              | y < yB = y
+                                                              | otherwise = go (y - 1)
+                                                    in go yT
+                                        in if yT' < yB' then
+                                             acc
+                                           else
+                                             go1 (acc + yT' - yB' + 1) (x + 1) yB' yT'
+      y0 = round cy
+      go0 !x | x > maxX = 0
+             | otherwise = if isInside x y0 then
+                             go1 0 x y0 y0
+                           else
+                             go0 (x + 1)
+  print $ go0 minX