1 {-# LANGUAGE NegativeLiterals #-}
2 {-# LANGUAGE FlexibleContexts #-}
3 {-# LANGUAGE OverloadedStrings #-}
4 {-# LANGUAGE TypeFamilies #-}
5 {-# LANGUAGE BangPatterns #-}
7 import Data.Text (Text)
8 import qualified Data.Text as T
9 import qualified Data.Text.IO as TIO
11 import Text.Megaparsec hiding (State)
12 import qualified Text.Megaparsec.Lexer as L
13 import Text.Megaparsec.Text (Parser)
14 import qualified Control.Applicative as CA
16 import qualified Data.Vector as V
20 import qualified Data.Set as S
23 type Vec = V.Vector Integer
25 data Particle = Particle
34 text <- TIO.readFile "data/advent20.txt"
35 let particles = successfulParse text
36 print $ part1 particles
37 print $ part2 50 particles
40 part1 :: [Particle] -> Int
41 part1 particles = head $ withMinX $ simulate particles
43 part2 :: Integer -> [Particle] -> Int
44 part2 n particles = length $ simulateC n particles
46 simulate :: [Particle] -> [Particle]
48 if all quiescent particles && length withMinXs == 1
50 else simulate (map step particles)
51 where withMinXs = withMinX particles
54 simulateC :: Integer -> [Particle] -> [Particle]
55 simulateC 0 particles = particles
56 simulateC t particles = simulateC (t - 1) (map step particles')
57 where particles' = removeColliders particles
60 step :: Particle -> Particle
61 step particle = particle {position = p', velocity = v'}
62 where pv' = V.zipWith3 updatePV (position particle)
64 (acceleration particle)
65 (p', v') = V.unzip pv'
66 updatePV p v a = (p + v + a, v + a)
69 -- Checks whether a particle could ever get closer to the origin than it is now.
70 quiescent :: Particle -> Bool
71 quiescent particle = and qDimensions
72 where qDimensions = V.zipWith3 sameSigns (position particle)
74 (acceleration particle)
75 sameSigns p v a = if a == 0 && v == 0
78 then signum p == signum v
79 else signum p == signum v
80 && signum v == signum a
83 withMinX particles = minX `elemIndices` absXs
84 where absXs = map pAbsX particles
87 pAbsX :: Particle -> Integer
88 pAbsX particle = V.foldl1' (+) $ V.map abs (position particle)
91 removeColliders particles = particles'
92 where positions = map position particles
93 duplicatePositions = S.fromList $ concat
94 $ filter (\g -> length g > 1)
97 particles' = filter (\p -> not (S.member (position p)
104 sc = L.space (skipSome spaceChar) CA.empty CA.empty
108 integer = lexeme L.integer
109 signedInteger = L.signed sc integer
112 separator = symbol ", "
115 particlesP = particleP `sepBy` space
116 particleP = particlify <$> (symbol "p=" *> vecP <* separator)
117 <*> (symbol "v=" *> vecP <* separator)
118 <*> (symbol "a=" *> vecP)
119 where particlify p v a = Particle { position = p
125 vecP = V.fromList <$> between (symbol "<") (symbol ">")
126 (signedInteger `sepBy` comma)
129 successfulParse :: Text -> [Particle]
130 successfulParse input =
131 case parse particlesP "input" input of
132 Left _error -> [] -- TIO.putStr $ T.pack $ parseErrorPretty err
133 Right instructions -> instructions