A company currently pays a fixed sum for the use of a particular licensed software package.   In determining if it has a good deal it decides to calculate its maximum use of the software from its license management log file.

Assume the software's licensing daemon faithfully records a checkout event when a copy of the software starts and a checkin event when the software finishes to its log file.

An example of checkout and checkin events are:

 License OUT @ 2008/10/03_23:51:05 for job 4974
 ...
 License IN  @ 2008/10/04_00:18:22 for job 4974



Task

Save the 10,000 line log file from    here   into a local file, then write a program to scan the file extracting both the maximum licenses that were out at any time, and the time(s) at which this occurs.

Mirror of log file available as a zip here (offsite mirror).




 
import Data.List
 
main = do
  f <- readFile "./../Puzzels/Rosetta/inout.txt"
  let (ioo,dt) = unzip. map ((\(_:io:_:t:_)-> (io,t)). words) . lines $ f
      cio = drop 1 . scanl (\c io -> if io == "IN" then pred c else succ c) 0 $ ioo 
      mo = maximum cio
  putStrLn $ "Maximum simultaneous license use is " ++ show mo ++ " at:"
  mapM_ (putStrLn . (dt!!)) . elemIndices mo $ cio
 