adventofcode1618/app/advent18f.hs

   1 module Main(main) where
   2
   3 import Data.List (tails, foldl')
   4
   5 -- input = "..^^."
   6 -- input = ".^^.^.^^^^"
   7 input = "^.^^^.^..^....^^....^^^^.^^.^...^^.^.^^.^^.^^..^.^...^.^..^.^^.^..^.....^^^.^.^^^..^^...^^^...^...^."
   8
   9 main :: IO ()
  10 main = do
  11         part1
  12         part2
  13
  14 part1 :: IO ()
  15 part1 = print $ fst $ foldl' nextRowFold (countSafe row, row) [2..40]
  16     where row = readRow input
  17
  18 part2 :: IO ()
  19 part2 = print $ fst $ foldl' nextRowFold (countSafe row, row) [2..400000]
  20     where row = readRow input
  21
  22 readRow :: String -> [Bool]
  23 readRow = map (=='^')
  24
  25 showRow :: [Bool] -> String
  26 showRow = map (\c -> if c then '^' else '.')
  27
  28 extended :: [Bool] -> [Bool]
  29 extended row = [False] ++ row ++ [False]
  30
  31 nextRow :: [Bool] -> [Bool]
  32 nextRow = map (isTrap) . segments . extended
  33
  34 nextRowFold :: (Int, [Bool]) -> Int -> (Int, [Bool])
  35 nextRowFold (n, row) _ = (n + countSafe newRow, newRow)
  36     where newRow = nextRow row
  37
  38 countSafe :: [Bool] -> Int
  39 countSafe = length . filter (not)
  40
  41 segments :: [a] -> [[a]]
  42 segments = filter ((==3) . length) . map (take 3) . tails
  43
  44 isTrap :: [Bool] -> Bool
  45 isTrap segment
  46     | segment == [True, True, False] = True
  47     | segment == [False, True, True] = True
  48     | segment == [True, False, False] = True
  49     | segment == [False, False, True] = True
  50     | otherwise = False