advent11h.hs

   1 -- Using the idea of canonical representation of buildings from
   2 -- https://andars.github.io/aoc_day11.html by Andrew Foote,
   3 -- plus my extension of represening the pairs as an integer.
   4
   5 -- This version is hillclimbing search, using a list for the agenda.
   6
   7 import Data.List (subsequences, (\\), sort, sortOn, nub, findIndices)
   8 import Data.Ord (comparing)
   9 import Data.Char (isDigit)
  10
  11 data Item = Generator String | Microchip String deriving (Show, Eq)
  12 type Floor = [Item]
  13 data Building = Building Int [Floor] deriving (Show, Eq)
  14 data CBuilding = CBuilding Int Integer deriving (Show, Eq)
  15 data Agendum = Agendum {current :: Building, trail :: [CBuilding], cost :: Int}
  16
  17 instance Ord Item where
  18     compare (Generator a) (Generator b) = compare a b
  19     compare (Microchip a) (Microchip b) = compare a b
  20     compare (Generator _) (Microchip _) = LT
  21     compare (Microchip _) (Generator _) = GT
  22
  23 instance Ord Building where
  24     compare b1 b2 = comparing estimateCost b1 b2
  25
  26 building1 = Building 0 [
  27     (sort [Generator "polonium", Generator "thulium",
  28      Microchip "thulium", Generator "promethium", Generator "ruthenium",
  29      Microchip "ruthenium", Generator "cobalt", Microchip "cobalt"]),
  30     (sort [Microchip "polonium", Microchip "promethium"]),
  31     [],
  32     []
  33     ]
  34
  35 building0 = Building 0 [
  36     (sort [Generator "polonium", Generator "thulium",
  37      Microchip "thulium", Generator "promethium"]),
  38     (sort [Microchip "polonium", Microchip "promethium"]),
  39     [],
  40     []
  41     ]
  42
  43 building2 = Building 0 [
  44     (sort [Generator "polonium", Generator "thulium",
  45      Microchip "thulium", Generator "promethium", Generator "ruthenium",
  46      Microchip "ruthenium", Generator "cobalt", Microchip "cobalt",
  47      Generator "elerium", Microchip "elerium",
  48      Generator "dilithium", Microchip "dilithium"]),
  49     (sort [Microchip "polonium", Microchip "promethium"]),
  50     [],
  51     []
  52     ]
  53
  54
  55 buildingTest = Building 0 [
  56     sort([Microchip "hydrogen", Microchip "lithium"]),
  57     [Generator "hydrogen"],
  58     [Generator "lithium"],
  59     []]
  60
  61 canonical :: Building -> CBuilding
  62 canonical (Building f floors) = CBuilding f (read $ filter (isDigit) $ show $ sort pairs)
  63     where names = nub $ map (\(Generator n) -> n) $ filter (isGenerator) $ concat floors
  64           floorOf (Generator g) = head (findIndices
  65                                                 (\fl -> (Generator g) `elem` fl)
  66                                                 floors)
  67           floorOf (Microchip g) = head (findIndices
  68                                                 (\fl -> (Microchip g) `elem` fl)
  69                                                 floors)
  70           pairs = foldl (\ps n -> (floorOf (Generator n), floorOf (Microchip n)):ps) [] names
  71
  72
  73
  74 main :: IO ()
  75 main = do
  76     part1
  77     part2
  78
  79
  80 part1 :: IO ()
  81 part1 = print $ length $ trail $ hillClimb (initAgenda building1) []
  82
  83 part2 :: IO ()
  84 part2 = print $ length $ trail $ hillClimb (initAgenda building2) []
  85
  86 initAgenda :: Building -> [Agendum]
  87 initAgenda b = [Agendum {current = b, trail=[], cost = estimateCost b}]
  88
  89 hillClimb :: [Agendum] -> [CBuilding] -> Agendum
  90 hillClimb [] _ = Agendum {current=buildingTest, trail=[], cost=0}
  91 hillClimb (currentAgendum:agenda) closed =
  92     if isGoal reached then currentAgendum
  93     else if creached `elem` closed
  94         then hillClimb agenda closed
  95         else hillClimb newAgenda (creached:closed)
  96     where
  97         reached = current currentAgendum
  98         creached = canonical reached
  99         newAgenda =
 100             sortOn (cost) $
 101             agenda ++ (candidates currentAgendum closed)
 102
 103
 104 candidates :: Agendum -> [CBuilding] -> [Agendum]
 105 candidates agendum closed = newCandidates
 106     where
 107         candidate = current agendum
 108         previous = trail agendum
 109         succs = legalSuccessors $ successors candidate
 110         excludable = previous ++ closed
 111         nonloops = filter (\s -> not $ (canonical s) `elem` excludable) succs
 112         newCandidates = map (\n -> makeAgendum n) nonloops
 113         makeAgendum new = Agendum {current = new,
 114                                     trail = (canonical candidate):previous,
 115                                     cost = estimateCost new}
 116
 117 isGoal :: Building -> Bool
 118 isGoal (Building f floors) =
 119     f+1 == height && (all (null) $ take f floors)
 120     where height = length floors
 121
 122 isLegal :: Building -> Bool
 123 isLegal (Building f floors) =
 124     null floor
 125     ||
 126     not (any (isGenerator) floor)
 127     ||
 128     any (safePair) pairs
 129     where floor = floors!!f
 130           pairs = [(i, j) | i <- floor, j <- floor, isGenerator i]
 131           safePair (Generator e, Microchip f) = e == f
 132           safePair (Generator _, Generator _) = False
 133
 134 isGenerator :: Item -> Bool
 135 isGenerator (Generator _) = True
 136 isGenerator (Microchip _) = False
 137
 138 successors :: Building -> [Building]
 139 successors (Building f floors) = [updateBuilding f floors nf is | nf <- nextFloors, is <- items]
 140     where
 141         floor = floors!!f
 142         items = filter (\is -> length is == 1 || length is == 2) $ subsequences floor
 143         nextFloors = if f == 0 then [1]
 144                      else if f+1 == length floors then [f-1]
 145                      else [f+1, f-1]
 146
 147 legalSuccessors :: [Building] -> [Building]
 148 legalSuccessors = filter (isLegal)
 149
 150 updateBuilding :: Int -> [Floor] -> Int -> [Item] -> Building
 151 updateBuilding oldF oldFloors newF items = Building newF newFloors
 152     where newFloors = map (updateFloor) $ zip [0..] oldFloors
 153           updateFloor (f, fl)
 154             | f == oldF = sort $ fl \\ items
 155             | f == newF = sort $ items ++ fl
 156             | otherwise = fl
 157
 158 estimateCost :: Building -> Int
 159 estimateCost (Building _ floors) =
 160     sum $ map (\(c, f) -> c * length f) $ zip [0..] $ reverse floors
 161