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-- requires cabal install --lib megaparsec parser-combinators
module Main (main) where
import Control.Monad (void, when)
import Data.List (foldl')
import Data.Map qualified as M
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
import System.Exit (die)
exampleExpectedOutput = 71
data Range = Range { field :: String
, ll :: Int
, lh :: Int
, hl :: Int
, hh :: Int
} deriving (Show)
type Ticket = [Int]
data Input = Input { ranges :: [Range]
, myTicket :: Ticket
, nearbyTickets :: [Ticket]
} deriving (Show)
type Parser = Parsec Void String
parseInt :: Parser Int
parseInt = do
n <- some digitChar
void $ optional (char ',')
return $ read n
parseRange :: Parser Range
parseRange = do
f <- some (letterChar <|> char ' ')
void $ string ": "
ll <- parseInt
void $ char '-'
lh <- parseInt
void $ string " or "
hl <- parseInt
void $ char '-'
hh <- parseInt
void $ char '\n'
return $ Range f ll lh hl hh
parseTicket :: Parser Ticket
parseTicket = some parseInt <* char '\n'
parseInput' :: Parser Input
parseInput' = do
r <- some parseRange
void $ string "\nyour ticket:\n"
t <- parseTicket
void $ string "\nnearby tickets:\n"
nts <- some parseTicket
void eof
return $ Input r t nts
parseInput :: String -> IO Input
parseInput filename = do
input <- readFile filename
case runParser parseInput' filename input of
Left bundle -> die $ errorBundlePretty bundle
Right ops -> return ops
compute :: Input -> Int
compute (Input ranges ticket nearbyTickets) = foldl' compute' 0 nearbyTickets
where
compute' :: Int -> Ticket -> Int
compute' acc nt = acc + (sum $ map isValid nt)
isValid :: Int -> Int
isValid n = minimum $ map (isValid' n) ranges
isValid' :: Int -> Range -> Int
isValid' n (Range{ll, lh, hl, hh})
| (n >= ll && n <= lh) || (n >= hl && n <= hh) = 0
| otherwise = n
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
|
