Project Euler Problem 075

import Data.List
import qualified Data.Map as M
d :: Integer
d=1500000 :: Integer
mapper :: Ord k => [k] -> Int
mapper l= M.size $ M.filter(==1) $ foldl' (\a c -> M.insertWith (+) c 1 a) M.empty l
ans1 :: Int
ans1 = mapper lis
       where
         lis = [ k*l |
                 m<-[2..ul],n<-[1..m], gcd m n==1, odd (m+n), --既約ピタゴラス数生成
                 let l=2*m*(m+n), --ここから、mは(sqrt (d/2))までで良い
                 k<-[1..(d`quot`l)]] -- k<-[1..d],k*l<=d相当
         ul = ((ceiling (sqrt $ fromIntegral (d`quot`2)))) --2m(m+n)からの枝かり
main :: IO ()
main = print ans1