aoc-2022/src/Days/D04.hs

module Days.D04 where

import Text.Megaparsec.Char as C (char)

import Common
import Parse (Parser, number, parsecDay, someLines)
import Util (count)

type Interval = (Int, Int)
type Intermediate = [(Interval, Interval)]

makeInterval :: (Ord a) => a -> a -> (a, a)
makeInterval a b
  | a > b = (b, a)
  | otherwise = (a, b)

parser :: Parser Intermediate
parser = someLines ((,) <$> interval <* char ',' <*> interval)
 where
  interval :: Parser Interval
  interval = makeInterval <$> number <* char '-' <*> number

contains :: Interval -> Interval -> Bool
contains (a, b) (c, d) = a <= c && b >= d

overlap :: Interval -> Interval -> Bool
overlap (a, b) (c, d) = not (b < c || a > d)

sym :: (a -> a -> Bool) -> (a -> a -> Bool)
sym f a b = f a b || f b a

part1 :: Intermediate -> Int
part1 = count (uncurry $ sym contains)

part2 :: Intermediate -> Int
part2 = count (uncurry overlap)

day :: Day
day = parsecDay parser (definitive . part1, definitive . part2)