AOC 2024 Day 3

Day3.hs

module Day3 where

import Data.List ( isPrefixOf )
import Data.List.Split ( splitOn )
import Data.Char ( isDigit )

run :: IO ()
run = do
    instructions <- readFile "./data/day3/input"
    let tuples = parseInstructions instructions
    print $ sum $ map (uncurry (*)) tuples

parseInstructions :: String -> [(Int, Int)]
parseInstructions [] = []
parseInstructions xs
    -- Comment this guard out for part one
    | "don't()" `isPrefixOf` xs = parseInstructions (dropUntil "do()" xs)
    | startsWithValid xs = extractValid xs : parseInstructions (tail $ dropWhile (')' /=) xs)
    | otherwise = parseInstructions (tail xs)

startsWithValid :: String -> Bool
startsWithValid xs = isPrefixOf "mul(" xs &&
                     all (all isDigit) (splitOn "," $ takeWhile (')' /=) $ drop (length "mul(") xs)

dropUntil :: String -> String -> String
dropUntil _ [] = []
dropUntil prefix xs
    | prefix `isPrefixOf` xs = xs
    | otherwise = dropUntil prefix (tail xs)

extractValid :: String -> (Int, Int)
extractValid xs = let
        [x, y] = splitOn "," $ takeWhile (')' /=) $ drop (length "mul(") xs
    in (read x, read y)