advent13.hs

   1 import Data.List ((\\), nub, sortOn)
   2 import Data.Bits (popCount)
   3
   4 type Pos = (Int, Int)
   5
   6 seed = 1362
   7
   8 goal1 = (31, 39)
   9
  10 main :: IO ()
  11 main = do
  12     part1
  13     part2
  14
  15
  16 part1 :: IO ()
  17 part1 = print $ length $ tail $ extractJust $ aStar [[(1, 1)]] []
  18
  19 part2 :: IO ()
  20 part2 = do print $ length $ tail $ edl 50 [[(1, 1)]] []
  21            putStrLn $ showRoomR 30 25 $ edl 50 [[(1, 1)]] []
  22
  23
  24 extractJust :: Maybe [a] -> [a]
  25 extractJust Nothing = []
  26 extractJust (Just x) = x
  27
  28 isWall :: Int -> Int -> Bool
  29 isWall x y = (popCount n) `mod` 2 == 1
  30     where
  31         n = x*x + 3*x + 2*x*y + y + y*y + seed
  32
  33
  34 showRoom w h = showRoomR w h []
  35
  36 showRoomR w h reached = unlines rows
  37     where
  38         rows = [row x | x <- [0..h]]
  39         row x = [showCell x y | y <- [0..w]]
  40         showCell x y = if (isWall x y)
  41             then '#'
  42             else if (x, y) `elem` reached
  43                 then 'O'
  44                 else '.'
  45
  46
  47 aStar :: [[Pos]] -> [Pos] -> Maybe [Pos]
  48 aStar [] _ = Nothing
  49 aStar (currentTrail:trails) closed =
  50     if isGoal (head currentTrail) then Just currentTrail
  51     else if (head currentTrail) `elem` closed then aStar trails closed
  52          else aStar newAgenda ((head currentTrail): closed)
  53     where newAgenda =
  54             sortOn (\a -> trailCost a) $
  55             trails ++ (candidates currentTrail closed)
  56           trailCost t = estimateCost (head t) + length t - 1
  57
  58
  59 -- exhaustive depth-limited
  60 edl :: Int -> [[Pos]] -> [Pos] -> [Pos]
  61 edl _ [] closed = nub closed
  62 edl limit (currentTrail:trails) closed =
  63     if (length currentTrail) > (limit+1) then edl limit trails ((head currentTrail):closed)
  64     else if (head currentTrail) `elem` closed then edl limit trails closed
  65          else edl limit newAgenda ((head currentTrail):closed)
  66     where newAgenda = trails ++ (candidates currentTrail closed)
  67
  68 candidates :: [Pos] -> [Pos] -> [[Pos]]
  69 candidates currentTrail closed = newCandidates
  70     where
  71         (candidate:trail) = currentTrail
  72         succs = legalSuccessors $ successors candidate
  73         nonloops = (succs \\ trail) \\ closed
  74         newCandidates = map (\n -> n:candidate:trail) nonloops
  75
  76 isGoal :: Pos -> Bool
  77 isGoal p = p == goal1
  78
  79 isLegal :: Pos -> Bool
  80 isLegal (x, y) =
  81     x >= 0 && y >= 0 && (not $ isWall x y)
  82
  83 successors :: Pos -> [Pos]
  84 successors (x, y) = [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]
  85
  86 legalSuccessors :: [Pos] -> [Pos]
  87 legalSuccessors = filter (isLegal)
  88
  89 estimateCost :: Pos -> Int
  90 estimateCost (x, y) = abs (x - gx) + abs (y - gy)
  91     where (gx, gy) = goal1
  92