Day_09(2023): solved

2023/Day_09/Day_09.hs

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+module Main where
+
+import System.Environment
+
+type Input = [[Int]]
+type Output = Int
+
+parseInput :: String -> Input
+parseInput = map (map read . words) . lines
+
+generateSubsequence :: [Int] -> [[Int]]
+generateSubsequence = takeWhile (not . all (== 0)) . iterate getDiffs
+    where getDiffs l = zipWith (-) (tail l) l
+
+partOne :: Input -> Output
+partOne = sum . map (foldr ((+) . last) 0 . generateSubsequence)
+
+partTwo :: Input -> Output
+partTwo = sum . map (foldr ((-) . head) 0 . generateSubsequence)
+
+compute :: Input -> String -> IO ()
+compute input "parse" = print input
+compute input "one"   = print . partOne $ input
+compute input "two"   = print . partTwo $ input
+compute input _       = error "Unknown part"
+
+main = do
+    args  <- getArgs
+    input <- parseInput <$> (readFile $ last args)
+    mapM (compute input)  $ init args 

2023/Day_09/README.md

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+## Day 09