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@UnkindPartition

UnkindPartition/contest.hs

Created October 12, 2014 09:30
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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
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