Project Euler 解答

Project Euler Problem 019

Project Euler Problem 019

import Data.List
-- 0:monday,1:tuesday,2:wednesday,3:thursday,4:friday,5:saturday,6:sunday
days :: [Integer]
days = concatMap (\x -> [31,28+leap x,31,30,31,30,31,31,30,31,30,31]) [1901..2000::Integer]
-- 365`rem`7が1901/01/01の曜日。init daysで2001/01/01の曜日を取り除く
daysl :: [Integer]
daysl = scanl (\a x -> (a+x)`rem`7) (365`rem`7) $ init days
leap :: (Integral a, Num a1) => a -> a1
leap n = if rem n 4 == 0 && rem n 100 /= 0 && rem n 400 == 0 then 1 else 0
ans1 :: Int
ans1 = length $ filter (==6) daysl
--171
main :: IO ()
main = print ans1

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