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
68
69
70
71
72
|
-- requires cabal install --lib megaparsec parser-combinators
module Main (main) where
import Control.Monad (void, when)
import Data.List (intersect, transpose)
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
import System.Exit (die)
exampleExpectedOutput = 20899048083289
type TileID = Int
data Tile = Tile { tileID :: TileID
, image :: [[Bool]]
, edgesPermutations :: [[Bool]]
} deriving Show
type Input = [Tile]
type Parser = Parsec Void String
parseInt :: Parser Int
parseInt = do
n <- some digitChar
return $ read n
parseLine :: Parser [Bool]
parseLine = do
elts <- some (char '#' <|> char '.')
void $ char '\n'
return $ map (== '#') elts
parseTile :: Parser Tile
parseTile = do
void $ string "Tile "
n <- parseInt
void $ string ":\n"
image <- some parseLine
let timage = transpose image
edges = [head image, last image, head timage, last timage]
inverted = map reverse edges
return $ Tile n image (edges ++ inverted)
parseInput' :: Parser Input
parseInput' = do
tiles <- some $ parseTile <* (optional $ char '\n')
void eof
return tiles
parseInput :: String -> IO Input
parseInput filename = do
input <- readFile filename
case runParser parseInput' filename input of
Left bundle -> die $ errorBundlePretty bundle
Right input' -> return input'
compute :: Input -> Int
compute tiles = product . map fst . filter ((== 4) . snd) $ map matchingEdges tiles
where
matchingEdges :: Tile -> (TileID, Int)
matchingEdges tile = (tileID tile, sum $ map (matches tile) tiles)
matches :: Tile -> Tile -> Int
matches Tile{tileID=a, image=_, edgesPermutations=e} Tile{tileID=b, image=_, edgesPermutations=f}
| a == b = 0
| otherwise = length $ intersect e f
main :: IO ()
main = do
example <- parseInput "example"
let exampleOutput = compute example
when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
input <- parseInput "input"
print $ compute input
|
