Problem 14
http://projecteuler.net/index.php?section=problems&id=14
--Haskell (needs -fbang-patterns -package containers), 20090101 import Data.Map (findMax, fromList) collatz :: Integer -> Integer collatz !n | n==1 = 1 | even n = 1 + collatz (n`div`2) | otherwise = 2 + collatz ((n*3+1)`div`2) main = print $ snd $ findMax $ fromList [(collatz (toInteger x), x) | x<-[1..999999]]
bang patternsを使わなければ,空間効率が悪すぎて終わらない.枝を刈ればもう少し速くなるだろう.
Problem 13
http://projecteuler.net/index.php?section=problems&id=13
--Haskell (Input data from STDIN), 20090101 main = getContents >>= print . take 10 . show . sum . map read . lines
Problem 12
http://projecteuler.net/index.php?section=problems&id=12
--Haskell, 20090104 import Sequence (trianglar) enprimes :: Int -> Int -> [Int] enprimes 1 _ = [] enprimes s n = let t = takeWhile ((==0).(s`mod`)) (iterate (*n) 1) in length t - 1 : enprimes (s`div`(last t)) (n+1) main = print $ head [x | x<-trianglar, (product.map (+1).enprimes x) 2 > 500]
数列モジュールを使用.改善の余地あり.
FizzBuzz
見かけたコードがおもしろかったので貼っておく.
http://d.hatena.ne.jp/takatoh/20070509/fizzbuzz