[Haskell-cafe] Slow IO?
stevech1097 at yahoo.com.au
Sun Aug 30 08:45:16 EDT 2009
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.
> 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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> > Haskell-Cafe at haskell.org
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