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Diffstat (limited to '')
-rw-r--r-- | 2020/12-Rain_Risk/second.hs | 66 |
1 files changed, 66 insertions, 0 deletions
diff --git a/2020/12-Rain_Risk/second.hs b/2020/12-Rain_Risk/second.hs new file mode 100644 index 0000000..c036def --- /dev/null +++ b/2020/12-Rain_Risk/second.hs @@ -0,0 +1,66 @@ +-- requires cabal install --lib megaparsec parser-combinators +module Main (main) where +import Control.Monad (void, when) +import Data.List (foldl') +import Data.Void (Void) +import Text.Megaparsec +import Text.Megaparsec.Char +import System.Exit (die) + +exampleExpectedOutput = 286 + +data Action = N | S | E | W | L | R | F +data Op = Op Action Int + +type Parser = Parsec Void String + +parseOp :: Parser Op +parseOp = do + action <- (char 'N' *> return N) + <|> (char 'S' *> return S) + <|> (char 'E' *> return E) + <|> (char 'W' *> return W) + <|> (char 'L' *> return L) + <|> (char 'R' *> return R) + <|> (char 'F' *> return F) + num <- some digitChar + void $ char '\n' + return $ Op action (read num) + +parseOps :: Parser [Op] +parseOps = some parseOp <* eof + +parseInput :: String -> IO [Op] +parseInput filename = do + input <- readFile filename + case runParser parseOps filename input of + Left bundle -> die $ errorBundlePretty bundle + Right ops -> return ops + +compute :: [Op]-> Int +compute ops = (\((x, y), _) -> abs(x)+abs(y)) $ foldl' step ((0, 0), (10, 1)) ops + where + step :: ((Int, Int), (Int, Int)) -> Op -> ((Int, Int), (Int, Int)) + step (p, (wx, wy)) (Op N i) = (p, (wx, wy+i)) + step (p, (wx, wy)) (Op S i) = (p, (wx, wy-i)) + step (p, (wx, wy)) (Op E i) = (p, (wx+i, wy)) + step (p, (wx, wy)) (Op W i) = (p, (wx-i, wy)) + step ((x, y), (wx, wy)) (Op F i) = ((x+i*wx, y+i*wy), (wx, wy)) + step (p, w) (Op a i) = (p, turn w a i) + turn :: (Int, Int) -> Action -> Int -> (Int, Int) + turn w a i = turn' w a mi + where mi = (i `mod` 360) `div` 90 + turn' (wx, wy) L 1 = (-wy, wx) + turn' (wx, wy) _ 2 = (-wx, -wy) + turn' (wx, wy) L 3 = (wy, -wx) + turn' (wx, wy) R 1 = (wy, -wx) + turn' (wx, wy) R 3 = (-wy, wx) + turn' w _ _ = w + +main :: IO () +main = do + example <- parseInput "example" + let exampleOutput = compute example + when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput) + input <- parseInput "input" + print $ compute input |