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author | Julien Dessaux | 2024-12-04 11:32:17 +0100 |
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committer | Julien Dessaux | 2024-12-04 11:32:17 +0100 |
commit | 4dee621ccf74908b4753ca54c13452d6b739a7f5 (patch) | |
tree | 13589fc43ad72c4782512abcd6e9c8f9266e4c0f /2024/04-Ceres_Search/first.hs | |
parent | 2024-03 in haskell (diff) | |
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2024-04 in haskell
Diffstat (limited to '2024/04-Ceres_Search/first.hs')
-rw-r--r-- | 2024/04-Ceres_Search/first.hs | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/2024/04-Ceres_Search/first.hs b/2024/04-Ceres_Search/first.hs new file mode 100644 index 0000000..673a45f --- /dev/null +++ b/2024/04-Ceres_Search/first.hs @@ -0,0 +1,51 @@ +-- requires cabal install --lib megaparsec parser-combinators heap vector +module Main (main) where + +import Control.Monad (void, when) +import qualified Data.List as L +import Data.Void (Void) +import Text.Megaparsec +import Text.Megaparsec.Char + +exampleExpectedOutput = 18 + +type Line = [Char] +type Input = [Line] + +type Parser = Parsec Void String + +parseInput' :: Parser Input +parseInput' = some (some letterChar <* 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' + +rotate90 = reverse . L.transpose +rotate180 = rotate90 . rotate90 + +diagonals = (++) <$> L.transpose . zipWith drop [0..] + <*> L.transpose . zipWith drop [1..] . rotate180 + +countInString :: String -> Int +countInString [] = 0 +countInString s@('X':'M':'A':'S':_) = 1 + (countInString $ tail s) +countInString s@('S':'A':'M':'X':_) = 1 + (countInString $ tail s) +countInString s = countInString $ tail s + +compute :: Input -> Int +compute lines = sum $ map countInString combinations + where + columns = rotate90 lines + combinations = lines ++ columns ++ diagonals lines ++ diagonals columns + +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 |