Problem 174

http://projecteuler.net/index.php?section=problems&id=174

まぁ、これもさっきと大して変わらない（と思う、もっと良い解法があるかも）。

import Data.List
import Data.Array.IO
n :: Integer
n = 10^6
lamina :: Integer -> [Integer]
lamina h = [l^2-h^2 | l <- [h+2,h+4..floor.sqrt.fromIntegral $ n + h^2]]
main :: IO ()
main = do l <- newArray (1,fromIntegral n)  :: IO (IOUArray Int Int)
mapM_ (incArray l).map fromIntegral.concatMap lamina $ [1..div n 2 - 2]
print.length.filter (x -> 1<=x && x<=10) =<< getElems l
where incArray ar x = readArray ar x >>= writeArray ar x.succ