[Haskell-beginners] Spoj BWHEELER problem - input problem
Artur Tadrała
artur.tadrala at gmail.com
Sat Jan 14 21:34:53 CET 2012
Hello
While learning Haskell I'm trying to solve some simple problems on
spoj.ploccasionally. 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
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