contest.hs

-- http://haskell98.blogspot.com/2014/10/blog-post_10.html

import Control.Monad

rotate n (x,y) = (n+1-y, x)
rotations n = take 4 $ iterate (rotate n .) id

solutions n =
  let half    = [ 1 .. n `div` 2 ]
      quarter = liftM2 (,) half half
  in mapM (\p -> rotations n `ap` [p]) quarter