> Hello
>
> While learning Haskell I'm trying to solve some simple problems on
spoj.pl
> occasionally. Currently I'm working on:
>
http://www.spoj.pl/problems/BWHEELER/. I figured out how to solve it but I
> have some problems with reading input (that's my guess)
>
> Here is my solution:
>
> import Data.List
> import Data.Array
> import qualified Data.ByteString.Lazy.Char8 as BS
> import IO
>
> traverse :: Array Int (Char, Int) -> Int -> Int -> String -> String
> traverse endings n k acc =
> let (c,i) = endings ! n
> in if k == 0
> then acc
> else traverse endings i (k-1) (c:acc)
>
> solve :: (Int, String) -> String
> solve (n,w) =
> let l = length w
> endings = sort $ zip w [0..]
> endingsArray = array (0, l) (zip [0..] endings)
> in reverse $ traverse endingsArray (n-1) l ""
>
> parseCases :: [BS.ByteString] -> [(Int, String)]
> parseCases (l:l':ls) =
> let n = readInt l
> w = BS.unpack l'
> in (n,w):parseCases ls
> parseCases _ = []
>
> main :: IO ()
> main = do
> ls <- BS.lines `fmap` (BS.readFile "input.txt")
> --BS.getContents
> putStr $ unlines $ map solve $ parseCases ls
>
> readInt :: BS.ByteString -> Int
> readInt x =
> case BS.readInt x of Just (i,_) -> i
> Nothing -> error ("Unparsable Int" ++ (show x))
>
>
> The input.txt file contains following text:
> 2
> bacab
> 3
> rwlb
> 11
> baaabaaaabbbaba
> 0
>
> When I compile and execute this code i get follwing output:
> aaaaaa
> lllll
> bbb
>
> It's different when compared to this in ghci ( this is what I expect):
> > map solve [(2,"bacab"), (3, "rwlb"), (11,"baaabaaaabbbaba")]
> ["abcba","rbwl","baaabbbbaaaaaab"]
>
> Can you explain me what I'm doing wrong?
> I appreciate any tips how to improve this code also.
>
> Thanks for help!
> Artur Tadrała
>