Solution for the second problem of the Google Code Jam 2014 Qualification Round

problem_b.hs

import System.Environment
import Control.Monad
import System.IO

calculateTime :: Double -> Double -> Double -> Double
calculateTime c f x = loop 2
    where loop rate
              | outright <= buying = outright
              | otherwise          = waiting + loop newRate
              where waiting  = c / rate
                    outright = x / rate
                    buying   = x / newRate + waiting
                    newRate  = rate + f

printResults :: Show a => Handle -> (a, String) -> IO ()
printResults output (i, cs) = hPutStrLn output $ "Case #" ++ show i ++ ": "
                              ++ show (calculateTime c f x)
    where [c,f,x] = map read $ words cs

main :: IO ()
main = do
  content <- getArgs >>= readFile . head
  let cases : eachCase = lines content
  withFile "output" WriteMode (\out -> zip [1..(read cases :: Int)] eachCase `forM_` printResults out)