day5

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

day5.hs

@@ -0,0 +1,37 @@
+import Lib (split)
+
+main :: IO ()
+main = do
+  input <- readFile "day5.in"
+  let [crates, cmds] = split "" $ lines input
+  let cratesList = init $ parseCrates $ init crates
+  let cmdsList = parseCmds cmds
+  putStr "Q1: "
+  print $ q1 cratesList cmdsList
+  putStr "Q2: "
+  print $ q2 cratesList cmdsList
+
+q1 :: [[Char]] -> [(Int, Int, Int)] -> [Char]
+q1 crates cmds = map head $ foldl (\x xs -> moveCrates x xs True) crates cmds
+
+q2 :: [[Char]] -> [(Int, Int, Int)] -> [Char]
+q2 crates cmds = map head $ foldl (\x xs -> moveCrates x xs False) crates cmds
+
+-- Computers are fast, really, not optimising right now
+moveCrates :: [[Char]] -> (Int, Int, Int) -> Bool -> [[Char]]
+moveCrates crates (n, a, b) rev =
+  let (head, tail) = splitAt n $ crates !! a
+   in replace b (replace a crates tail) ((if rev then reverse head else head) ++ crates !! b)
+  where
+    replace :: Int -> [a] -> a -> [a]
+    replace i xs x = take i xs ++ [x] ++ drop (i + 1) xs
+
+parseCrates :: [[Char]] -> [[Char]]
+parseCrates ([] : _) = [[]]
+parseCrates crates = parseCrate crates : parseCrates (map (drop 4) crates)
+  where
+    parseCrate :: [[Char]] -> [Char]
+    parseCrate = foldr (\(_ : x : _ : _) xs -> if x /= ' ' then x : xs else xs) []
+
+parseCmds :: [[Char]] -> [(Int, Int, Int)]
+parseCmds = foldr (\x xs -> let y = split ' ' x in (read $ y !! 1, read (y !! 3) - 1, read (y !! 5) - 1) : xs) []