aoc-2024-haskell/day1/Main.hs

module Main where

import System.Environment (getArgs)

import Data.List (sort)
import Data.Function (on)

import Text.Parsec (parse, many, char, endBy)
import Text.ParserCombinators.Parsec (GenParser)
import Text.ParserCombinators.Parsec.Number (decimal)

line :: GenParser Char st (Int, Int)
line = decimal >>= \l -> many (char ' ') >> decimal >>= \r -> return (l, r)

locationIDs :: GenParser Char st [(Int, Int)]
locationIDs = endBy line (char '\n')

part1 :: [Int] -> [Int] -> Int
part1 l r = sum (zipWith (curry (abs . uncurry (-))) l r)

part2 :: [Int] -> [Int] -> Int
part2 l r = (sum . map (\x -> sum ((map (const x) . filter (==x)) r))) l

main :: IO ()
main = do
    args <- getArgs
    (fp:_) <- return args
    content <- readFile fp
    case parse locationIDs fp content of
        Left e -> putStrLn ("Input file is incorrectly formatted : " ++ show e)
        Right ids -> do
            let (ls, rs) = uncurry ((,) `on` sort) (unzip ids)
            putStrLn ("Solution (Part 1) : " ++ show (part1 ls rs))
            putStrLn ("Solution (Part 2) : " ++ show (part2 ls rs))