import           Data.List.Split (splitOn)

lineSafe' :: [Int] -> Bool
lineSafe' [] = True
lineSafe'
  l@(_:xs) = (all (> 0) diffs || all (< 0) diffs) && all validItem diffs
  where
    diffs = zipWith (-) xs l

    validItem x = x /= 0 && abs x <= 3

allRemoved :: [a] -> [[a]]
allRemoved [] = []
allRemoved (x:xs) = xs:map (x:) (allRemoved xs)

lineSafe :: [Int] -> Bool
lineSafe = any lineSafe' . allRemoved

main :: IO ()
main = print . length . filter testLine . lines =<< readFile "data.txt"
  where
    testLine = lineSafe . map read . splitOn " "