Project Euler 解答

Project Euler Problem 051

Project Euler Problem 051

import Data.Char import Data.List import Data.Maybe primes :: [Integer] primes = 2:f [3] [3,5..] where f (x:xs) ys = ps ++ f (xs++ps) [z | z<-qs,z`rem`x/=0] where (ps,qs) = span (< x*x) ys isPrime :: Integer -> Bool isPrime 1 = False isPrime nn = imp nn primes where imp n (x:xs) = if x*x>n then True else if rem n x==0 then False else imp n xs sdigs :: [Integer] sdigs = filter same $ dropWhile (<56003) primes where same n = r /= nub r where r = show n sames :: Integer -> String sames n = imp (show n) [] where imp [] acc = acc imp (x:xs) acc = case elem x xs of True -> imp (filter (/=x) xs) (x:acc) False -> imp xs acc --同じ数字を置き換えて作れる素数の個数をかえす --複数パターンがある場合はその最大値をかえす trial :: Integer -> Int trial p = count $ map (length.filter (\x -> isPrime x && (length $ show x)==(length $ show p))) r where count [] = 0 count x = maximum x s2i n = foldl (\a x -> 10*a+x) 0 n sp = show p fromlist = sames p tolist = map intToDigit [0..9] r = map (\from -> map (\to -> s2i $ map (fromIntegral.digitToInt) $ imp sp from to) tolist) fromlist --impは置き換えるだけ imp :: String -> Char -> Char -> String imp [] _ _ = [] imp (x:xs) from to = if x==from then to:imp xs from to else x:imp xs from to ans1 :: Integer ans1 = fromJust $ find ((==8).trial) primes --121313 main :: IO () main = print ans1

since 2013