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．

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 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 11

http://projecteuler.net/index.php?section=problems&id=11
traih.log様のSmartなコードを参考に．

--Haskell (Input data from STDIN), 20090101

import List (tails, transpose)

horizon, diagonal :: [[Int]] -> Int
horizon = maximum . map (maximum . map (product . take 4) . tails)
diagonal = horizon . transpose . zipWith drop [0..]

process :: [[Int]] -> Int
process = maximum . flip map [horizon, horizon.transpose, diagonal, diagonal.(map reverse)] . flip ($)

main = getContents >>= print . process . map (map read . words) . lines

Problem 1

http://projecteuler.net/index.php?section=problems&id=1

--Haskell, 20090101

main = print $ sum $ [x | x<-[1..999], x`mod`3==0||x`mod`5==0]

Problem 2

http://projecteuler.net/index.php?section=problems&id=2

--Haskell, 20090104

import Sequence (fibonacci)

main = print $ sum [x | x<-takeWhile (<=4000000) fibonacci, even x]

数列モジュールを使用．

Problem 3

http://projecteuler.net/index.php?section=problems&id=3

--Haskell, 20090101

divide :: Integer -> Integer -> Integer
divide 1 n = n
divide t n = if t`mod`n==0 then divide (t`div`n) n
                           else divide t (n+1)

main = print $ divide 600851475143 2