Haskell Quiz/Sampling/Solution Dolio
This is a somewhat naive algorithm, but it manages to run the challenge problem in a reasonable amount of time. It simply uses the IntSet data structure, testing and adding random numbers until enough are found.
module Main where import qualified Data.IntSet as I import System import System.Random build n k s (r:rs) | k `seq` s `seq` False = undefined -- strictness | k >= n = s | not $ I.member r s = build n (k+1) (I.insert r s) rs | otherwise = build n k s rs main = do [n, l] <- fmap (map read) getArgs g <- getStdGen if n > l then putStrLn "Your request is impossible." else putStr . unlines . map show . I.elems $ build n 0 I.empty (randomRs (0, l-1) g)
A run of the sample problem on my machine took about 1 minute.