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author | Julien Dessaux | 2023-12-09 18:28:43 +0100 |
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committer | Julien Dessaux | 2023-12-09 18:28:43 +0100 |
commit | 95417d3684bd31bdc3e603cbdbaf441cdea191da (patch) | |
tree | 0b11827f088069d13b147bac4df72e716d5cf868 /2023/09-Mirage_Maintenance/second.hs | |
parent | 2023-08 in haskell (diff) | |
download | advent-of-code-95417d3684bd31bdc3e603cbdbaf441cdea191da.tar.gz advent-of-code-95417d3684bd31bdc3e603cbdbaf441cdea191da.tar.bz2 advent-of-code-95417d3684bd31bdc3e603cbdbaf441cdea191da.zip |
2023-09 in haskell
Diffstat (limited to '')
-rw-r--r-- | 2023/09-Mirage_Maintenance/second.hs | 53 |
1 files changed, 53 insertions, 0 deletions
diff --git a/2023/09-Mirage_Maintenance/second.hs b/2023/09-Mirage_Maintenance/second.hs new file mode 100644 index 0000000..77e9b97 --- /dev/null +++ b/2023/09-Mirage_Maintenance/second.hs @@ -0,0 +1,53 @@ +-- requires cabal install --lib megaparsec parser-combinators +module Main (main) where + +import Control.Applicative.Permutations +import Control.Monad (void, when) +import Data.Char qualified as C +import Data.Either +import Data.Functor +import Data.List qualified as L +import Data.Map qualified as M +import Data.Maybe +import Data.Set qualified as S +import Data.Void (Void) +import Text.Megaparsec +import Text.Megaparsec.Char + +import Debug.Trace + +exampleExpectedOutput = 2 + +type History = [Int] +type Input = [History] + +type Parser = Parsec Void String + +parseNumber :: Parser Int +parseNumber = read <$> some (char '-' <|> digitChar) <* hspace + +parseInput' :: Parser Input +parseInput' = some (some parseNumber <* eol) <* eof + +parseInput :: String -> IO Input +parseInput filename = do + input <- readFile filename + case runParser parseInput' filename input of + Left bundle -> error $ errorBundlePretty bundle + Right input' -> return input' + +compute :: Input -> Int +compute = sum . map (next . reverse) + where + next :: History -> Int + next = sum . map last . takeWhile (any (/= 0)) . iterate differences + differences :: History -> History + differences xs = zipWith (flip (-)) xs (tail xs) + +main :: IO () +main = do + example <- parseInput "example" + let exampleOutput = compute example + when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput) + input <- parseInput "input" + print $ compute input |