aoc/app/2.hs

{-# LANGUAGE LambdaCase, MultiWayIf #-}
module Main where

import Data.Functor

parse :: String -> [[Int]]
parse = ((read <$>) . words <$>) . lines

solve1 :: [[Int]] -> Int
solve1 =
  let di a = all (\a' -> a' <  4 && not (a' <= 0)) a ||
             all (\a' -> a' > -4 && not (a' >= 0)) a in
  sum . ((\a -> if di $ zipWith (flip (-)) a (tail a) then 1 else 0) <$>)

solve2 :: [[Int]] -> Int
solve2 =
  let r [] = [[]]
      r (r':rs) = rs:((r':) <$> r rs) in
  sum . ((\a -> if a > 0 then 1 else 0) . solve1  .
         r <$>)

main :: IO ()
main = readFile "inputs/2" <&> parse >>= \i ->
       print (solve1 i) >>
       print (solve2 i)