From 3ae71a6adaf7cb9249a1a610c228e8ac84afab6d Mon Sep 17 00:00:00 2001 From: Joe Zhao Date: Wed, 18 Mar 2015 15:09:18 +0800 Subject: +20 +21 +22 +23 +24 +25 --- h23.hs | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) create mode 100644 h23.hs (limited to 'h23.hs') diff --git a/h23.hs b/h23.hs new file mode 100644 index 0000000..f85a87a --- /dev/null +++ b/h23.hs @@ -0,0 +1,21 @@ +import System.Random +import Data.List + +rnd_select :: [a] -> Int -> IO [a] +rnd_select _ 0 = return [] +rnd_select (x:xs) n = + do + r <- randomRIO (0, (length xs)) + if r < n + then do + rest <- rnd_select xs (n-1) + return (x : rest) + else rnd_select xs n + +rnd_select' xs n = do + gen <- getStdGen + return $ take n [ xs !! x | x <- randomRs (0, (length xs) - 1) gen] + +rnd_select'' :: Int -> [a] -> [a] +rnd_select'' n x = map (x!!) is + where is = take n . nub $ randomRs (0, length x - 1) (mkStdGen 100) -- cgit v1.2.3-70-g09d2