AoC/2020/day02/day02.hs

import Data.List.Split

main :: IO ()
main = do
  input <- lines <$> readFile "input"
  print $ day2 f1 input
  print $ day2 f2 input

day2 :: (String -> Int -> Int -> Char -> Bool) -> [String] -> Int
day2 f = length . filter (predicate f)

f1 :: String -> Int -> Int -> Char -> Bool
f1 str a b c = (l >= a) && (l <= b)
  where
    l = length $ filter (== c) str

f2 :: String -> Int -> Int -> Char -> Bool
f2 str a b c = (str !! pred a == c) /= (str !! pred b == c)

predicate :: (String -> Int -> Int -> Char -> Bool) -> String -> Bool
predicate f line = f str a b c
  where
    c = head $ words p !! 1
    [a, b] = map read $ splitOn "-" $ head $ words p
    [p, str] = splitOn ": " line