advent01/Main.hs

   1 -- Writeup at https://work.njae.me.uk/2023/12/01/advent-of-code-2023-day-01/
   2
   3 import AoC
   4 import Data.Char
   5 import Data.List
   6
   7 main :: IO ()
   8 main =
   9   do  dataFileName <- getDataFileName
  10       cals <- readFile dataFileName
  11       let calibrations = lines cals
  12       print $ part1 calibrations
  13       print $ part2 calibrations
  14
  15 part1 :: [String] -> Int
  16 -- part1 calibrations = sum $ fmap getCalibration calibrations
  17 part1  = sum . (fmap getCalibration)
  18
  19 part2 :: [String] -> Int
  20 part2 calibrations = sum $ fmap (getCalibration . replaceNums) calibrations
  21
  22 getCalibration :: String -> Int
  23 getCalibration calibration = read [head digits, last digits]
  24   where digits = filter isDigit calibration
  25
  26 replaceNums :: String -> String
  27 replaceNums haystack = reverse $ foldl' go "" $ tails haystack
  28   where go acc [] = acc
  29         go acc xs
  30           | "one"   `isPrefixOf` xs = '1' : acc
  31           | "two"   `isPrefixOf` xs = '2' : acc
  32           | "three" `isPrefixOf` xs = '3' : acc
  33           | "four"  `isPrefixOf` xs = '4' : acc
  34           | "five"  `isPrefixOf` xs = '5' : acc
  35           | "six"   `isPrefixOf` xs = '6' : acc
  36           | "seven" `isPrefixOf` xs = '7' : acc
  37           | "eight" `isPrefixOf` xs = '8' : acc
  38           | "nine"  `isPrefixOf` xs = '9' : acc
  39           | isDigit (head xs) = (head xs) : acc
  40           | otherwise = acc