[Haskell/2023/09] Add solution

Haskell/2023/09.hs

@@ -0,0 +1,21 @@
+import Lib
+
+type Input = [[Int]]
+
+main :: IO ()
+main = aoc 2023 9 setup solve1 solve2 ["1"]
+
+solve1 :: Input -> Int
+solve1 = sum . map solve
+
+solve2 :: Input -> Int
+solve2 = sum . map (solve . reverse)
+
+solve :: [Int] -> Int
+solve = sum . map last . takeWhile (any (/= 0)) . iterate step
+
+step :: [Int] -> [Int]
+step = zipWith (-) =<< tail
+
+setup :: String -> Input
+setup = map (map read . words) . lines