Data commit

Task/Cut-a-rectangle/Haskell/cut-a-rectangle.hs

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+import qualified Data.Vector.Unboxed.Mutable as V
+import Data.STRef
+import Control.Monad (forM_, when)
+import Control.Monad.ST
+
+dir :: [(Int, Int)]
+dir = [(1, 0), (-1, 0), (0, -1), (0, 1)]
+
+data Env = Env { w, h, len, count, ret :: !Int, next :: ![Int] }
+
+cutIt :: STRef s Env -> ST s ()
+cutIt env = do
+    e <- readSTRef env
+    when (odd $ h e) $ modifySTRef env $ \en -> en { h = w e,
+        w = h e }
+    e <- readSTRef env
+    if odd (h e)
+        then modifySTRef env $ \en -> en { ret = 0 }
+        else
+            if w e == 1
+            then modifySTRef env $ \en -> en { ret = 1 }
+            else do
+                let blen = (h e + 1) * (w e + 1) - 1
+                    t = (h e `div` 2) * (w e + 1) + (w e `div` 2)
+                modifySTRef env $ \en -> en { len = blen,
+                    count = 0,
+                    next = [ w e + 1, (negate $ w e) - 1, -1, 1] }
+                grid <- V.replicate (blen + 1) False
+                case odd (w e) of
+                    True -> do
+                        V.write grid t True
+                        V.write grid (t + 1) True
+                        walk grid (h e `div` 2) (w e `div` 2 - 1)
+                        e1 <- readSTRef env
+                        let res1 = count e1
+                        modifySTRef env $ \en -> en { count = 0 }
+                        walk grid (h e `div` 2 - 1) (w e `div` 2)
+                        modifySTRef env $ \en -> en { ret = res1 +
+                            (count en * 2) }
+                    False -> do
+                        V.write grid t True
+                        walk grid (h e `div` 2) (w e `div` 2 - 1)
+                        e2 <- readSTRef env
+                        let count2 = count e2
+                        if h e == w e
+                            then modifySTRef env $ \en -> en { ret =
+                                count2 * 2 }
+                            else do
+                                walk grid (h e `div` 2 - 1)
+                                    (w e `div` 2)
+                                modifySTRef env $ \en -> en { ret =
+                                    count en }
+    where
+        walk grid y x = do
+            e <- readSTRef env
+            if y <= 0 || y >= h e || x <= 0 || x >= w e
+                then modifySTRef env $ \en -> en { count = count en + 1 }
+                else do
+                    let t = y * (w e + 1) + x
+                    V.write grid t True
+                    V.write grid (len e - t) True
+                    forM_ (zip (next e) [0..3]) $ \(n, d) -> do
+                        g <- V.read grid (t + n)
+                        when (not g) $
+                            walk grid (y + fst (dir !! d)) (x + snd (dir !! d))
+                    V.write grid t False
+                    V.write grid (len e - t) False
+
+cut :: (Int, Int) -> Int
+cut (x, y) = runST $ do
+    env <- newSTRef $ Env { w = y, h = x, len = 0, count = 0, ret = 0, next = [] }
+    cutIt env
+    result <- readSTRef env
+    return $ ret result
+
+main :: IO ()
+main = do
+    mapM_ (\(x, y) -> when (even (x * y)) (putStrLn $
+        show x ++ " x " ++ show y ++ ": " ++ show (cut (x, y))))
+        [ (x, y) | x <- [1..10], y <- [1..x] ]