advent06/Main.hs

   1 -- Writeup at https://work.njae.me.uk/2022/12/06/advent-of-code-2022-day-6/
   2
   3 import AoC
   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 part1 :: String -> Int
  18 part1 = interestingPosition 4
  19
  20 part2 :: String -> Int
  21 part2 = interestingPosition 14
  22
  23 interestingPosition :: Int -> String -> Int
  24 interestingPosition n text = n + (fst packetPos)
  25   where candidates = zip [0..] $ fmap (take n) $ tails text
  26         packetPos = head $ dropWhile (hasSame . snd) candidates
  27
  28 allDifferent, hasSame :: String -> Bool
  29 allDifferent cs = nub cs == cs
  30 hasSame = not . allDifferent