aoc/app/7.hs

module Main where

import Data.Functor

data D = D { target :: Int, parts :: [Int]}

parse :: String -> [D]
parse = ((\(a:as) -> D (read $ takeWhile (/= ':') a) (read <$> as)) . words <$>) . lines

canBeTarget :: Int -> [Int -> Int -> Int] -> [Int] -> Bool
canBeTarget _ _ []       = False
canBeTarget t _ [x]      = t == x
canBeTarget t o (x:y:xs) = any (canBeTarget t o . (:xs)) ((uncurry <$> o) <*> pure (x,y))

solve1 :: [D] -> Int
solve1 = sum . (target <$>) . filter (\(D t p) -> canBeTarget t [(*), (+)] p)

solve2 :: [D] -> Int
solve2 =  sum . (target <$>) . filter (\(D t p) -> canBeTarget t [(*), (+), \a b -> read (show a ++ show b)] p)

main :: IO ()
main = readFile "inputs/7" <&> parse >>= \i ->
       print (solve1 i)
       >> print (solve2 i)