Day_15(2023): solved

2023/Day_15/Day_15.hs

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+module Main where
+
+import Data.Char
+import Data.List.Split
+import Data.Map (Map, (!), adjust, fromList, toList)
+import System.Environment
+
+data Lens = Lens { label :: String, focal :: Int } deriving (Show)
+type Boxes = Map Int [Lens]
+
+type Input = [String]
+type Output = Int
+
+parseInput :: String -> Input
+parseInput = splitOn "," . head . lines
+
+getHash :: String -> Int
+getHash = foldl (\acc x -> (acc + ord x) * 17 `rem` 256) 0
+
+putInBoxes :: Boxes -> String -> Boxes
+putInBoxes boxes = go . span (`notElem` "=-")
+    where go (lab, "-"    ) = adjust (filter ((/= lab) . label)) (getHash lab) boxes
+          go (lab, '=' : n) | lab `elem` labels     = adjust (const $ before ++ [Lens lab (read n)] ++ after) hash boxes
+                            | otherwise             = adjust (Lens lab (read n) :) hash boxes
+                            where hash              = getHash lab
+                                  elements          = boxes ! getHash lab
+                                  labels            = map label elements
+                                  (before, _:after) = span ((/= lab) . label) elements
+
+partOne :: Input -> Output
+partOne = sum . map getHash
+
+partTwo :: Input -> Output
+partTwo = sum . map getPower . toList . foldl putInBoxes (fromList [(i, []) | i <- [0 .. 255]])
+    where getPower (i, xs) = sum [(i + 1) * j * focal lens | (j, lens) <- zip [1 .. ] $ reverse xs]
+
+compute :: Input -> String -> IO ()
+compute input "parse" = print input
+compute input "one"   = print . partOne $ input
+compute input "two"   = print . partTwo $ input
+compute input _       = error "Unknown part"
+
+main = do
+    args  <- getArgs
+    input <- parseInput <$> readFile (last args)
+    mapM (compute input) $  init args 

2023/Day_15/README.md

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+## Day 15