[Haskell-cafe] Slow IO?

[Steve]

On Sun, 2009-08-30 at 14:40 +0400, Eugene Kirpichov wrote:
Thanks, that works nicely too. However, I believe its not a standard
package, so I don't think it can be used for Sphere Online problems.

I timed a test run on a 10MB file and its a little slower than my
solution with the ByteString readInt improvement.

Steve

> 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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> >
> 
> 
>