day 8

8-a.hs

@@ -0,0 +1,32 @@
+{-# LANGUAGE TupleSections #-}
+
+import Data.List
+
+-- this is literally only a function because read is stupid
+parse :: String -> [[Int]]
+parse = map (map (read . singleton)) . lines
+
+getGridSize :: [[a]] -> (Int, Int)
+getGridSize grid = (length $ head grid, length grid)
+
+isVisible :: [[Int]] -> (Int, Int) -> Bool
+isVisible grid (x, y) = any startStep [(-1, 0), (1, 0), (0, -1), (0, 1)]
+  where startGridValue = grid !! y !! x
+        (gridWidth, gridHeight) = getGridSize grid
+        startStep (facingX, facingY) = isVisible' (x + facingX, y + facingY) (facingX, facingY)
+        isVisible' (gridX, gridY) (facingX, facingY)
+          | gridX < 0 || gridY < 0 || gridX > (gridWidth - 1) || gridY > (gridHeight - 1) = True
+          | otherwise = (grid !! gridY !! gridX) < startGridValue
+            && isVisible' (gridX + facingX, gridY + facingY) (facingX, facingY)
+
+listPermutations :: [a] -> [a] -> [(a, a)]
+listPermutations a = concatMap (\b' -> map (, b') a)
+
+getAllCoordinates grid = listPermutations [0..gridWidth-1] [0..gridHeight-1]
+  where (gridWidth, gridHeight) = getGridSize grid
+
+main = interact $
+  show
+  . length . filter id
+  . (\grid -> map (isVisible grid) $ getAllCoordinates grid)
+  . parse

8-b.hs

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+{-# LANGUAGE TupleSections #-}
+import Data.List
+
+parse :: String -> [[Int]]
+parse = map (map (read . singleton)) . lines
+
+getGridSize :: [[a]] -> (Int, Int)
+getGridSize grid = (length $ head grid, length grid)
+
+getScenicScore :: [[Int]] -> (Int, Int) -> Int
+getScenicScore grid (x, y) = product $ map startStep [(-1, 0), (1, 0), (0, -1), (0, 1)]
+  where startGridValue = grid !! y !! x
+        (gridWidth, gridHeight) = getGridSize grid
+        startStep (facingX, facingY) = scenicScoreStep (x + facingX, y + facingY) (facingX, facingY)
+        scenicScoreStep (gridX, gridY) (facingX, facingY)
+          | gridX < 0 || gridY < 0 || gridX > (gridWidth - 1) || gridY > (gridHeight - 1) = 0
+          | (grid !! gridY !! gridX) < startGridValue = 1 + scenicScoreStep (gridX + facingX, gridY + facingY) (facingX, facingY)
+          | otherwise = 1
+
+listPermutations :: [a] -> [a] -> [(a, a)]
+listPermutations a = concatMap (\b' -> map (, b') a)
+
+getAllCoordinates grid = listPermutations [0..gridWidth-1] [0..gridHeight-1]
+  where (gridWidth, gridHeight) = getGridSize grid
+
+main = interact $
+  show
+  . maximum
+  . (\grid -> map (getScenicScore grid) $ getAllCoordinates grid)
+  . parse