[Haskell-cafe] Slow IO?

[Eugene Kirpichov]

module Main where

import qualified Data.ByteString.Lazy as B
import Data.ByteString.Nums.Careless -- from bytestring-nums package

bint :: B.ByteString -> Int
bint = int

main = do
  line : rest <- B.split 10 `fmap` B.getContents
  let [n, k] = map int . B.split 32 $ line
  putStrLn . show . length . tail . filter ((==0).(`mod`k).bint)  $ rest

This does a 100MB file in 2.7s (probably because the file is cached by
the filesystem).

2009/8/30 Steve <stevech1097 at yahoo.com.au>:
> Hi,
> I'm tackling a Sphere Online Judge tutorial question where it tests how
> fast you can process input data. You need to achieve at least 2.5MB of
> input data per second at runtime (on an old machine running ghc 6.6.1).
> This is probably close to the limit of Haskell's ability.
>
> https://www.spoj.pl/problems/INTEST/
>
> I can see that 24 haskell programmers have solved it, but most are very
> close to the 8 secs limit (and 6/24 are even over the limit!).
>
> Here's my code. It fails with a "time limit exceeded" error. (I think it
> would calculate the correct result, eventually).
>
> module Main where
>
> import qualified Data.List as DLi
> import qualified System.IO as SIO
>
> main :: IO ()
> main = do
>  line1 <- SIO.hGetLine SIO.stdin
>  let k = read $ words line1 !! 1
>  s <- SIO.hGetContents SIO.stdin
>  print $ count s k
>
> count :: String -> Int -> Int
> count s k = DLi.foldl' foldFunc 0 (map read $ words s)
>  where
>    foldFunc :: Int -> Int -> Int
>    foldFunc a b
>      | mod b k == 0  = a+1
>      | otherwise     = a
>
>
> I tried using Data.ByteString but then found that 'read' needs a String,
> not a ByteString.
> I tried using buffered IO, but it did not make any difference.
>
> Any suggestions on how to speed it up?
>
> Regards,
> Steve
>
> _______________________________________________
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>



-- 
Eugene Kirpichov
Web IR developer, market.yandex.ru