http://www.codechef.com/problems/PERMUT2/ #2

gistfile1.hs

import Data.Char (ord)
import qualified Data.Map as Map
import qualified Data.ByteString as BS

main :: IO ()
main = BS.getContents >>=
	mapM_ (putStrLn . fmt . isAmbiguous . parse) . skipN . BS.split nl
	where
	nl = fromIntegral $ ord '\n'
	fmt True  = "ambiguous"
	fmt False = "unambiguous"

skipN :: [a] -> [a]
skipN (_:x:xs) = x : skipN xs
skipN [] = []
skipN _ = []

parse :: BS.ByteString -> [Int]
parse = map readIt . BS.split (fromIntegral $ ord ' ')
	where
	readIt = BS.foldl (\n d -> n * 10 + (fromIntegral d - ord '0')) 0

isAmbiguous :: [Int] -> Bool
isAmbiguous = snd . foldl (\(m,a) (i,v) ->
		case i `compare` v of
			EQ -> (m, a)
			LT -> (Map.insert i v m, a)
			GT -> (m, a && Just i == Map.lookup v m)
	) (Map.empty, True) . zip [1..]