Project Euler 解答

Project Euler Problem 057

Project Euler Problem 057

import Control.Arrow
import Data.Array
import Data.Ratio
-- メモ化
n :: Integer
n = 1000
nth_ :: Array Integer (Ratio Integer)
nth_ = a where
  a = listArray (1,n) ((3%2): [nth i | i <- [2..n] ])
  nth m = 1 + ((denominator (a!(m-1))) % (denominator (a!(m-1)) + numerator (a!(m-1))))
ans1 :: Int
ans1 = length $ filter (uncurry(>).((length . show . numerator)&&&(length . show . denominator))) $ take 1000 $ elems nth_
--153
main :: IO ()
main = print ans1

since 2013