1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
|
module Day24A where
import System.Environment (getArgs)
import Data.List (elemIndex)
import qualified Data.Map.Strict as M;
-- Types
data Direction = E | SE | SW | W | NW | NE
deriving (Eq, Show);
data Colour = White | Black
deriving (Eq, Show);
type Coord = (Int, Int, Int);
type Grid = M.Map Coord Colour;
inverse :: Colour -> Colour
inverse White = Black
inverse Black = White
-- Parsing
parseDirections :: String -> [Direction]
parseDirections "" = []
parseDirections ('e':xs) = E : parseDirections xs
parseDirections ('w':xs) = W : parseDirections xs
parseDirections ('s':'e':xs) = SE : parseDirections xs
parseDirections ('s':'w':xs) = SW : parseDirections xs
parseDirections ('n':'e':xs) = NE : parseDirections xs
parseDirections ('n':'w':xs) = NW : parseDirections xs
parseDirections _ = error "Invalid directions"
parseFile :: String -> IO [[Direction]]
parseFile f = do
c <- readFile f;
return $ map parseDirections $ lines c;
-- Grid manipulation
flipTile :: Grid -> Coord -> Grid
flipTile g c = M.insert c (inverse $ M.findWithDefault White c g) g
baseCoord :: Coord
baseCoord = (0, 0, 0)
followDirections :: Coord -> [Direction] -> Coord
followDirections c [] = c
followDirections (x, y, z) (E:ds) = followDirections (x + 1, y - 1, z) ds
followDirections (x, y, z) (W:ds) = followDirections (x - 1, y + 1, z) ds
followDirections (x, y, z) (NE:ds) = followDirections (x + 1, y, z - 1) ds
followDirections (x, y, z) (NW:ds) = followDirections (x, y + 1, z - 1) ds
followDirections (x, y, z) (SE:ds) = followDirections (x, y - 1, z + 1) ds
followDirections (x, y, z) (SW:ds) = followDirections (x - 1, y, z + 1) ds
flipByDirections :: [Direction] -> Grid -> Grid
flipByDirections ds g = flipTile g $ followDirections baseCoord ds
-- Usage: runghc 24a.hs inputs/day24
main :: IO ()
main = do
args <- getArgs;
ds <- parseFile $ head args;
let final = foldr flipByDirections M.empty ds;
let blacks = M.size $ M.filter (== Black) final;
print blacks;
return ();
|
