task27.hs

{-# LANGUAGE FlexibleContexts #-}
import Control.Monad
import Control.Monad.ST
import Control.Exception 
import System.Random
import Data.Functor

import qualified Data.Vector.Generic.Mutable as V
import qualified Data.Vector.Unboxed as U

m = 120
 
task27 :: [Int] -> (Int, Int)
task27 l = runST $ do 
    r <- V.replicate m 0 :: ST s (U.MVector s Int)

    let go []     = return (1,2)
        go (a:as) = do
          let p = a `mod` m
          cur_lead <- r `V.read` p
          when (a > cur_lead) (V.write r p a)
          go as
    go l

randTest :: 
  Int -> -- Length of random testing sequence
  IO ()
randTest n =
  newStdGen <&>
  randoms <&> 
  take n <&> 
  task27 >>=
  print

main = randTest 1000000