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AoC 2022 #09

Dec 9th, 2022
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  1. {-# OPTIONS_GHC -Wno-incomplete-patterns #-}
  2.  
  3. import Data.List (nub) -- remove duplicates
  4. import Data.List.Split (splitOn)
  5.  
  6. main :: IO ()
  7. main = do
  8.   f <- readFile "input01.txt"
  9.   print $ taskOne f
  10.   print $ taskTwo f
  11.  
  12. taskOne :: String -> Int
  13. taskOne = length . nub . snd . foldl moveRope (replicate 2 (0, 0), [(0, 0)]) . concatMap parseMove . lines
  14.  
  15. taskTwo :: String -> Int
  16. taskTwo = length . nub . snd . foldl moveRope (replicate 10 (0, 0), [(0, 0)]) . concatMap parseMove . lines
  17.  
  18. data Move = U | L | D | R deriving (Show, Eq)
  19.  
  20. moveRope :: ([(Int, Int)], [(Int, Int)]) -> Move -> ([(Int, Int)], [(Int, Int)])
  21. moveRope (rope, tailTrail) move = (rope', tailTrail')
  22.   where
  23.     headPos' = (moveHead move . head) rope
  24.    rope' = (scanl moveTail headPos' . tail) rope
  25.    tailTrail' = last rope' : tailTrail
  26.  
  27. moveHead :: Move -> (Int, Int) -> (Int, Int)
  28. moveHead U (x, y) = (x, y + 1)
  29. moveHead L (x, y) = (x - 1, y)
  30. moveHead D (x, y) = (x, y - 1)
  31. moveHead R (x, y) = (x + 1, y)
  32.  
  33. moveTail :: (Int, Int) -> (Int, Int) -> (Int, Int)
  34. moveTail (xHead, yHead) (xTail, yTail)
  35.  | abs (xHead - xTail) <= 1 && abs (yHead - yTail) <= 1 = (xTail, yTail) -- head and tail are adjacent or on the same position -> no tail movement
  36.  | xHead == xTail && yHead > yTail = (xTail, yTail + 1) -- same column, head over tail
  37.  | xHead == xTail && yHead < yTail = (xTail, yTail - 1) -- same column, head under tail
  38.  | yHead == yTail && xHead > xTail = (xTail + 1, yTail) -- same row, head right of tail
  39.  | yHead == yTail && xHead < xTail = (xTail - 1, yTail) -- same row, head left of tail
  40.  | xHead > xTail && yHead > yTail = (xTail + 1, yTail + 1) -- head top right of tail
  41.  | xHead < xTail && yHead > yTail = (xTail - 1, yTail + 1) -- head top left of tail
  42.  | xHead < xTail && yHead < yTail = (xTail - 1, yTail - 1) -- head down left of tail
  43.  | xHead > xTail && yHead < yTail = (xTail + 1, yTail - 1) -- head down right of tail
  44.  
  45. parseMove :: String -> [Move]
  46. parseMove line
  47.  | direction == 'U' = replicate steps U
  48.  | direction == 'L' = replicate steps L
  49.  | direction == 'D' = replicate steps D
  50.  | direction == 'R' = replicate steps R
  51.  where
  52.    direction = (head . head) split
  53.    steps = ((\x -> read x :: Int) . last) split
  54.    split = splitOn " " line
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