advent03/src/advent03part1.hs

   1 import Data.Text (Text)
   2 import qualified Data.Text.IO as TIO
   3
   4 import Data.Void (Void)
   5
   6 import Text.Megaparsec hiding (State)
   7 import Text.Megaparsec.Char
   8 import qualified Text.Megaparsec.Char.Lexer as L
   9 import qualified Control.Applicative as CA
  10
  11 import Data.List (foldl', foldl1')
  12 import qualified Data.Set as S
  13
  14 import Linear (V2(..), (^+^), (^-^), (*^), (*^))
  15
  16 data Direction = East | South | West | North deriving (Show, Eq)
  17
  18 type Location = V2 Int -- x, y
  19
  20 type Visited = S.Set Location
  21
  22 data Path = Path { _visited :: Visited
  23                  , _tip :: Location
  24                  }
  25                deriving (Show, Eq)
  26
  27 data Segment = Segment { _direction :: Direction
  28                        , _steps :: Int
  29                        } deriving (Show, Eq)
  30
  31
  32 main :: IO ()
  33 main = do
  34         text <- TIO.readFile "data/advent03.txt"
  35         let segmentss = successfulParse text
  36         -- print segmentss
  37         -- print $ travelPath $ head segmentss
  38         print $ part1 segmentss
  39         -- print $ part2 machine
  40
  41 part1 :: [[Segment]] -> Int
  42 part1 segmentss = closest $ crossovers $ travelAllPaths segmentss
  43
  44 closest :: Visited -> Int
  45 closest points = S.findMin $ S.map manhattan points
  46
  47 crossovers :: [Path] -> Visited
  48 crossovers travelledPaths =
  49       foldl1' S.intersection $ map _visited travelledPaths
  50
  51 travelAllPaths :: [[Segment]] -> [Path]
  52 travelAllPaths = map travelPath
  53
  54 travelPath :: [Segment] -> Path
  55 travelPath segments = foldl' travelSegment path0 segments
  56     where   path0 = Path { _visited = S.empty, _tip = V2 0 0 }
  57
  58 travelSegment :: Path -> Segment -> Path
  59 travelSegment path segment = path { _tip = tip', _visited = visited' }
  60     where   delta = facing $ _direction segment
  61             distance = _steps segment
  62             start = _tip path
  63             visited = _visited path
  64             visited' = foldl' (flip S.insert) visited $ take distance $ drop 1 $ iterate (^+^ delta) start
  65             tip' = start ^+^ distance *^ delta
  66
  67 facing :: Direction -> Location
  68 facing East = V2 1 0
  69 facing South = V2 0 (-1)
  70 facing West = V2 (-1) 0
  71 facing North = V2 0 1
  72
  73
  74 manhattan (V2 x y) = (abs x) + (abs y)
  75
  76 -- Parse the input file
  77 type Parser = Parsec Void Text
  78
  79 sc :: Parser ()
  80 sc = L.space (skipSome spaceChar) CA.empty CA.empty
  81 -- sc = L.space (skipSome (char ' ')) CA.empty CA.empty
  82
  83 lexeme  = L.lexeme sc
  84 integer = lexeme L.decimal
  85 -- signedInteger = L.signed sc integer
  86 symb = L.symbol sc
  87 comma = symb ","
  88
  89 wiresP = many pathP
  90 pathP = segmentP `sepBy1` comma
  91
  92 segmentP = segmentify <$> directionP <*> integer
  93     where segmentify direction steps =
  94               Segment { _direction = direction, _steps = steps }
  95
  96
  97 directionP = eP <|> sP <|> wP <|> nP
  98 eP = (symb "R" *> pure East)
  99 sP = (symb "D" *> pure South)
 100 wP = (symb "L" *> pure West)
 101 nP = (symb "U" *> pure North)
 102
 103
 104 successfulParse :: Text -> [[Segment]]
 105 successfulParse input =
 106         case parse wiresP "input" input of
 107                 Left  _err -> [] -- TIO.putStr $ T.pack $ parseErrorPretty err
 108                 Right wires -> wires