2024 day 4

2024/4/Main1.hs

@@ -0,0 +1,23 @@
+import           Data.List (isPrefixOf, transpose)
+import           Data.Universe.Helpers (diagonals)
+
+countTimes :: String -> String -> Int
+countTimes _ [] = 0
+countTimes s fullLine@(_:nextLine)
+  | s `isPrefixOf` fullLine = 1 + countTimes s (drop (length s) fullLine)
+  | otherwise = countTimes s nextLine
+
+countHoriz :: String -> Int
+countHoriz l = countTimes "XMAS" l + countTimes "SAMX" l
+
+countLines :: [String] -> Int
+countLines = sum . map countHoriz
+
+countAll :: [String] -> Int
+countAll ls = countLines ls
+  + countLines (transpose ls)
+  + countLines (diagonals ls)
+  + countLines (diagonals (reverse ls))
+
+main :: IO ()
+main = print . countAll . lines =<< readFile "data.txt"

2024/4/Main2.hs

@@ -0,0 +1,36 @@
+import qualified Data.Vector as V
+
+isMas :: (Char, Char) -> Bool
+isMas x = x == ('M', 'S') || x == ('S', 'M')
+
+noEnds :: V.Vector a -> Int -> Int -> Int
+noEnds v i
+  | i == 0 || i == V.length v - 1 = const 0
+  | otherwise = id
+
+countAll :: V.Vector (V.Vector Char) -> Int
+countAll v = V.ifoldl'
+  (\acc x l -> acc
+   + noEnds
+     v
+     x
+     (V.ifoldl'
+        (\acc2 y c -> acc2
+         + noEnds
+           l
+           y
+           (if getAt x y == 'A'
+              && (isMas (getAt (x - 1) (y - 1), getAt (x + 1) (y + 1))
+                  && isMas (getAt (x + 1) (y - 1), getAt (x - 1) (y + 1)))
+            then 1
+            else 0))
+        0
+        l))
+  0
+  v
+  where
+    getAt x y = v V.! x V.! y
+
+main :: IO ()
+main = print . countAll . V.fromList . map V.fromList . lines
+  =<< readFile "data.txt"

flake.nix

@@ -39,6 +39,7 @@
                 text
                 text-icu
                 unordered-containers
+                universe-base
                 vector
               ]))
           ];