Day01-2.hs

module Main where

removePlus :: String -> String
removePlus = filter (/= '+')

toInts :: String -> [Int]
toInts = map ((read :: String -> Int) . removePlus) . lines

solve :: [Int] -> Int
solve xs = go [0] xs
  where
    go acc [] = go acc xs
    go acc@(a:_) (y:ys) =
      if elem (y + a) acc
        then (y + a)
        else go ((y + a) : acc) ys

main :: IO ()
main = do
  text <- readFile "input.txt"
  putStrLn $ show $ solve $ toInts text