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author | Julien Dessaux | 2024-12-07 13:56:28 +0100 |
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committer | Julien Dessaux | 2024-12-07 13:56:28 +0100 |
commit | 4c205242a592e022f28c7881e0f230db065b9cfc (patch) | |
tree | 4b018753318e1a5efe5b0c51cd764e24af47f23b /2024/07-Bridge_Repair/first.hs | |
parent | 2024-01 in factor (diff) | |
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2024-07 in haskell
Diffstat (limited to '2024/07-Bridge_Repair/first.hs')
-rw-r--r-- | 2024/07-Bridge_Repair/first.hs | 50 |
1 files changed, 50 insertions, 0 deletions
diff --git a/2024/07-Bridge_Repair/first.hs b/2024/07-Bridge_Repair/first.hs new file mode 100644 index 0000000..ba85958 --- /dev/null +++ b/2024/07-Bridge_Repair/first.hs @@ -0,0 +1,50 @@ +-- requires cabal install --lib megaparsec parser-combinators heap vector +module Main (main) where + +import Control.Applicative.Permutations +import Control.Monad (void, when) +import Data.Void (Void) +import Text.Megaparsec +import Text.Megaparsec.Char + +exampleExpectedOutput = 3749 + +data Equation = Equation Int [Int] deriving Show +type Input = [Equation] + +type Parser = Parsec Void String + +parseNumber :: Parser Int +parseNumber = read <$> some digitChar <* optional hspace + +parseEquation :: Parser Equation +parseEquation = Equation <$> parseNumber <* string ": " + <*> some parseNumber + +parseInput' :: Parser Input +parseInput' = some (parseEquation <* 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 total . filter valid + where + total (Equation t _) = t + valid (Equation total numbers) = elem total $ combinations numbers + combinations [x] = [x] + combinations l = let x = last l + xs = init l + in concatMap (\n -> [x+n, x*n]) $ combinations 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 |