aoc2021/app/D4P2.hs

module Main where

main :: IO ()
main = interact solution

type Board = [[Int]]

scnd :: (b -> c) -> (a, b) -> (a, c)
scnd f (a, b) = (a, f b)

frst :: (a -> c) -> (a, b) -> (c, b)
frst f (a, b) = (f a, b)

solution :: String -> String
solution =
  show
  -- ([Int], [Boards])
  . scnd toBoards
  . scnd (map (map (read :: String -> Int)))
  . scnd (filter (not . null))
  . scnd (map words)
  . frst (map (read :: String -> Int))
  . frst splitcomma
  . (\x -> (head x, tail x))
  . lines
  where
    splitcomma :: String -> [String] -- "stole" the implementation from `words`
    splitcomma s = case dropWhile (==',') s of
      "" -> []
      s' -> w : splitcomma s''
        where
          (w, s'') = break (==',') s'      

toBoards :: [[Int]] -> [Board]
toBoards [] = []
toBoards (a:b:c:d:e:r) = [a,b,c,d,e]:toBoards r