advent06/Main.hs

   1 -- Writeup at https://work.njae.me.uk/2022/12/06/advent-of-code-2022-day-6/
   2
   3 import System.Environment
   4 import Data.List
   5
   6 -- test = "mjqjpqmgbljsphdztnvjfqwrcgsmlb"
   7
   8 main :: IO ()
   9 main =
  10   do  dataFileName <- getDataFileName
  11       text <- readFile dataFileName
  12       -- print $ part1 test
  13       -- print $ part2 test
  14       print $ part1 text
  15       print $ part2 text
  16
  17 getDataFileName :: IO String
  18 getDataFileName =
  19   do args <- getArgs
  20      progName <- getProgName
  21      let baseDataName =  if null args
  22                          then progName
  23                          else head args
  24      let dataFileName = "data/" ++ baseDataName ++ ".txt"
  25      return dataFileName
  26
  27 part1 :: String -> Int
  28 part1 = interestingPosition 4
  29
  30 part2 :: String -> Int
  31 part2 = interestingPosition 14
  32
  33 interestingPosition :: Int -> String -> Int
  34 interestingPosition n text = n + (fst packetPos)
  35   where candidates = zip [0..] $ fmap (take n) $ tails text
  36         packetPos = head $ dropWhile (hasSame . snd) candidates
  37
  38 allDifferent, hasSame :: String -> Bool
  39 allDifferent cs = nub cs == cs
  40 hasSame = not . allDifferent