Day 9

Day9.hs

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+module Day9 where
+import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
+import Data.Char (digitToInt)
+
+columns :: String -> Int
+columns str = maximum $ map length $ lines str
+
+indexOr :: Int -> [a] -> a -> a
+indexOr i list j
+    | i `elem` [0..length list] = list !! i
+    | otherwise                 = j
+
+compNeighbors :: [Int] -> Int -> Int -> [Int]
+compNeighbors ints i width = [middle | all (middle <) [left, right, top, bottom]]
+    where middle = ints !! i
+          left   = getLeft (i - 1)
+          right  = getRight (i + 1)
+          top    = indexOr (i - width) ints 9
+          bottom = indexOr (i + width) ints 9
+          -- make sure that we aren't wrapping around the line edge
+          getLeft  x = if (i `mod` width) == 0 then 9 else indexOr (x :: Int) ints 9
+          getRight x = if (i `mod` width) == (width - 1) then 9 else indexOr (x :: Int) ints 9
+
+main :: IO ()
+main = do
+    input <- openFile "inputs/9.txt" ReadMode
+    contents <- hGetContents input
+
+    let width = columns contents
+    let ints = digitToInt <$> concat (lines contents)
+    
+    print . sum . map ((+1) . head) . filter (/= []) $ [compNeighbors ints x width | x <- [0..length ints - 1]]
+
+    hClose input

Day9_1.hs

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+module Day9_1 where
+import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
+import Data.Char (digitToInt)
+import Data.List (sort)
+
+-- i gave up on my original solution
+-- this isn't very original and is influcenced by other people's solutions
+-- i'm sorry
+
+columns :: String -> Int
+columns str = maximum $ map length $ lines str
+
+xy :: Int -> Int -> [[Int]] -> (Int, Int) -> Int
+xy w h arr (x, y)
+    | x < 0 || x >= w = 9
+    | y < 0 || y >= h = 9
+    | otherwise = arr !! y !! x 
+
+-- left, right, up, down from current coord
+neigh :: (Int, Int) -> [(Int, Int)]
+neigh (x, y) = [(x - 1, y), (x + 1, y), (x, y - 1), (x, y + 1)]
+
+basin :: Int -> Int -> [[Int]] -> [(Int, Int)] -> [(Int, Int)] -> [(Int, Int)]
+basin w h ints acc [] = acc
+basin w h ints acc (x:xs)
+    | pos x == 9 || x `elem` acc = basin w h ints acc xs
+    | otherwise = basin w h ints (x:acc) (xs ++ neigh x)
+    where pos = xy w h ints
+
+main :: IO ()
+main = do
+    input <- openFile "inputs/9.txt" ReadMode
+    contents <- hGetContents input
+
+    let ints = map (map digitToInt) $ lines contents
+
+    let width = columns contents
+    let height = length ints
+
+    let coordMap = [ (x, y) | x <- [0..width-1], y <- [0..height-1] ]
+    let pos = xy width height ints
+
+    let lowest = [ coord | coord <- coordMap, and [neighbor > pos coord | neighbor <- pos <$> neigh coord] ]
+
+    print . product . take 3 . reverse . sort $ map (length . basin width height ints [] . pure) lowest
+
+    hClose input