dojo13b.hs

import qualified Data.Vector as V (Vector(..),fromList,toList, (//), (!), foldl')

candidates :: Int -> V.Vector Int
candidates n = (V.fromList [2..n]) V.// filters
  where filters = concat $ map (\x -> isMult x n) [2..n]

isMult :: Int -> Int -> [(Int,Int)]
isMult x u = [(x*m-2,0) | m <- [2..(u `div` x)]]

rotations :: Int -> [Int]
rotations x = map read $ filter (\x -> head x /= '0') $ take l (iterate step (show x))
  where l = length (show x)

step :: String -> String
step (x:xs) = xs ++ [x]

check :: V.Vector Int -> Int -> [(Int,Int)]
check acc x = if and (map (\x -> 1 < acc V.! x) rs) then [] else zip rs (repeat 0)
  where rs = map (+ (-2)) $ rotations x

circular :: Int -> V.Vector Int
circular x = circular' cVec cList
  where circular' acc xs = acc V.// (concat $ map (check cVec) xs)
        cVec = candidates x
        cList = V.toList cVec

val = V.foldl' foldStep 0 (circular 1000000)
  where foldStep x y = if y > 1 then x + 1 else x



main :: IO ()
main = print val