Reading lots of input.

Attoparsec.hs

-- | Timing breakdown:
--     Reading: 2.5s
--     Sorting: 3.5s

module Main where

import Control.Applicative
import Control.Monad
import Data.ByteString.Char8 (pack)
import Data.Attoparsec.ByteString.Char8
import Data.Functor
import Data.List

doLinearTimeStuffWith :: Int -> [Int] -> IO ()
doLinearTimeStuffWith n ns = print (ns !! (n - 1))

parseIntList :: Int -> Parser [Int]
parseIntList n = count n (signed decimal <* endOfLine)

main = do
  n <- readLn :: IO Int
  ns <- parseOnly (parseIntList n) . pack <$> getContents
  case ns of
   Left err  -> print err
   Right ns' -> doLinearTimeStuffWith n $ sort ns'

ReplicateM.hs

module Main where

import Control.Monad
import Data.List

doLinearTimeStuffWith :: Int -> [Int] -> IO ()
doLinearTimeStuffWith n ns = print (ns !! (n - 1))

main = do
  n <- readLn :: IO Int
  ns <- replicateM n (readLn :: IO Int)
  doLinearTimeStuffWith n $ sort ns