all tasks

Task/Spiral-matrix/Haskell/spiral-matrix.hs

@@ -0,0 +1,12 @@
+module Spiral where
+
+import Data.List
+import Control.Monad
+import Control.Monad.Instances
+
+grade xs = map snd. sort $ zip xs [0..]
+values n = cycle [1,n,-1,-n]
+counts n = (n:).concatMap (ap (:) return)  $ [n-1,n-2..1]
+reshape n = unfoldr (\xs -> if null xs then Nothing else Just (splitAt n xs))
+
+spiral n = reshape n . grade. scanl1 (+). concat $ zipWith replicate (counts n) (values n)