練習問題/解答例/Haskell/練習問題解答例の履歴(No.9)

変な処理があれば修正してください。

ループ1†

times 0 action = return ()
times n action = action >> times (n-1) action

main = do
    5 `times` putStrLn "Hello World!"

別解

main = putStr $ "おっぱい！" >> "Hello World!\n"

↑

ループ2†

問題文

import System.Environment

times 0 action = return ()
times n action = action >> times (n-1) action

main = do
    x <- getArgs
    (read (x !! 0)) `times` putStrLn "Hello World!"

↑

FizzBuzz†

問題文

main = do
    mapM_ putStrLn (map fizzBuzz [1..100])

fizzBuzz :: Integer -> String
fizzBuzz n
    | n `mod` 15 == 0 = "FizzBuzz"
    | n `mod`  5 == 0 = "Buzz"
    | n `mod`  3 == 0 = "Fizz"
    | otherwise       = show n

↑

素数列挙†

問題文

primesTo m = 2 : sieve [3, 5..m] where
    sieve [] = []
    sieve (p:xs) = p : sieve (xs `minus` [p*p, p*p+2*p..m])

minus (x:xs) (y:ys) = case (compare x y) of
    LT -> x : minus xs (y:ys)
    EQ ->     minus xs ys
    GT ->     minus (x:xs) ys
minus xs _ = xs

main = do
    print $ primesTo (floor 1e6)

↑

うるう年判定†

問題文

isleap :: Integer -> Bool
isleap y
    | y `mod` 400 == 0 = True
    | y `mod` 100 == 0 = False
    | y `mod`   4 == 0 = True
    | otherwise        = False

main = do
    putStrLn "西暦を入力してください"
    x <- getLine
    putStrLn (x ++ "年はうるう年" ++ if isleap(read(x)) then "です" else "ではありません" )

↑

フィボナッチ数列†

問題文

import System.Environment

fibo = 0 : 1 : zipWith (+) fibo (tail fibo)

main = do
    x <- getArgs
    putStrLn (show (fibo !! read (x !! 0)))

↑

累乗1†

問題文

pow :: Integer -> Integer -> Integer
pow _ 0 = 1
pow 0 _ = 0
pow a b = a * pow a (b-1)

main = do
    putStrLn (show (pow 2 10))

↑

累乗2†

問題文

pow :: Integer -> Integer -> Integer
pow 0 _ = 0
pow _ 0 = 1
pow a b = pow' 1 a b
    where
    pow' x a 0 = x
    pow' x a b
        | even b = pow' x (a*a) (div b 2)
        | otherwise = pow' (x*a) a (b-1)

main = do
    putStrLn (show (pow 2 1000007))

↑

クイックソート†

問題文

quicksort :: (Ord a) => [a] -> [a]
quicksort [] = []
quicksort (x:xs) =
    let smallerSorted = quicksort[a | a<-xs, a <= x]
        biggerSorted  = quicksort[a | a<-xs, a >  x]
     in smallerSorted ++ [x] ++ biggerSorted

main :: IO()
main = print $ quicksort [5, 7, 9, 2, 1, 3, 8, 4, 6, 0]

↑

世界のナベアツ問題†

問題文

nabeatsu :: Integer -> String
nabeatsu x = if mod x 3 == 0 || elem '3' s then "Aho" else s where s = show x

main :: IO ()
main = putStrLn . unwords $ map nabeatsu [1..100]

↑

Caesar暗号解読†

問題文

import Data.List (isInfixOf)
 
next :: String -> Char -> Char
next (x:xs) = \c -> if x == c then head xs else next xs c
next _ = id
 
analyze :: String -> String
analyze = head . filter (isInfixOf keyword) . iterate (map $ next chars)
    where chars   = "-abcdefghijklmnopqrstuvwxyz .,-"
          keyword = "person"
 
main :: IO ()
main =  putStrLn $ analyze encoded
    where encoded = "qdq-gi.q-a ziatmxxitmdqibtqi-ustbi ri.qmoqrcxi.qbubu zir -ibtq\
                    \i-qp-qaai ripmymsqkir -ibtqi-qy dmxi ri.cnxuoi rruoumxakir -ib\
                    \tqiqzmobyqzbkii-q.qmxi -imyqzpyqzbi rixmeaki -puzmzoqai -i-qsc\
                    \xmbu zaimzpir -i btq-iymbbq-a;iz -iatmxximzgi.q-a zinqiuzimzgi\
                    \emgipuao-uyuzmbqpimsmuzabir -ia. za -uzsiacotiimi.qbubu zj"

練習問題/解答例/Haskell/練習問題解答例 の履歴(No.9)

ループ1†

ループ2†

FizzBuzz†

素数列挙†

うるう年判定†

フィボナッチ数列†

累乗1†

累乗2†

クイックソート†

世界のナベアツ問題†

Caesar暗号解読†