src/advent02/advent02.hs

   1 import Data.List
   2
   3
   4 main :: IO ()
   5 main = do
   6         text <- readFile "data/advent02.txt"
   7         let ids = lines text
   8         print $ part1 ids
   9         putStrLn $ part2 ids
  10
  11 part1 ids = (fst counts23) * (snd counts23)
  12     where allLetterCounts = map letterCounts ids
  13           counts23 = foldl' addCounts (0, 0) allLetterCounts
  14
  15 letterCounts :: String -> [Int]
  16 letterCounts = map length . group . sort
  17
  18 addCounts :: (Int, Int) -> [Int] -> (Int, Int)
  19 addCounts (twos, threes) counts = (twos', threes')
  20     where twos'   = if has2 counts then twos + 1   else twos
  21           threes' = if has3 counts then threes + 1 else threes
  22
  23 has2 = elem 2
  24 has3 = elem 3
  25
  26 part2 ids = uncurry sameChars closeIds
  27     where closeIds = head $ filter (\ab -> uncurry differenceCount ab == 1) [(a, b) | a <- ids, b <- ids]
  28
  29 differenceCount :: String -> String -> Int
  30 differenceCount this that = length $ filter (\(a, b) -> a /= b) $ zip this that
  31
  32 sameChars :: String -> String -> String
  33 sameChars this that = map fst $ filter (\(a, b) -> a == b) $ zip this that
  34