reddit towers benchmark

towers

import Criterion.Main
import System.Random
import Data.List
import qualified Data.Vector.Unboxed as U

rainfall1 :: [Int] -> Int
rainfall1 xs = sum (zipWith (-) mins xs)
  where
    mins = zipWith min maxl maxr
    maxl = scanl1 max xs
    maxr = scanr1 max xs

rainfall2 :: U.Vector Int -> Int
rainfall2 xs = U.sum (U.zipWith (-) mins xs)
  where
    mins = U.zipWith min maxl maxr
    maxl = U.scanl1' max xs
    maxr = U.scanr1' max xs

-- Our benchmark harness.
main = do
  g <- getStdGen
  let hs = take 10000000 (randomRs (0, 200) g :: [Int])
  defaultMain [
    bgroup "rainfall" [
        bench "rainfall1" $ whnf rainfall1 hs,
        bench "rainfall2" $ whnf rainfall2 (U.fromList hs)
        ]
    ]