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Print the final position for reference #98

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Dec 16, 2024
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Print the final position for reference #98

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36 changes: 26 additions & 10 deletions hs/src/Day14.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,13 +7,15 @@

import Common (groupConsecutiveBy)
import Control.Monad (join, liftM2)
import Data.Char (intToDigit)
import Data.Map qualified as Map (findWithDefault)
import Data.Map.Strict qualified as Map (fromListWith)
import Data.Ord (Down (Down))
import Data.Set qualified as Set (fromList, toList)
import Data.String (IsString)
import Data.Text (Text)
import Data.Void (Void)
import Debug.Trace (traceM)
import Text.Megaparsec (MonadParsec, ParseErrorBundle, Stream (Token, Tokens), parse, sepEndBy1)
import Text.Megaparsec.Char (char, newline, string)
import Text.Megaparsec.Char.Lexer qualified as L (decimal, signed)
Expand All @@ -22,7 +24,7 @@
parser = line `sepEndBy1` newline
where
line = (,) <$> (string "p=" *> v2) <*> (string " v=" *> v2)
v2 = (,) <$> (L.signed (pure ()) L.decimal <* char ',') <*> (L.signed (pure ()) L.decimal)

Check warning on line 27 in hs/src/Day14.hs

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Suggestion in parser in module Day14: Redundant bracket ▫︎ Found: "(,) <$> (L.signed (pure ()) L.decimal <* char ',')\n <*> (L.signed (pure ()) L.decimal)" ▫︎ Perhaps: "(,) <$> (L.signed (pure ()) L.decimal <* char ',')\n <*> L.signed (pure ()) L.decimal"

part1 :: Text -> Either (ParseErrorBundle Text Void) Int
part1 = part1' 101 103
Expand All @@ -44,16 +46,30 @@
part2 :: Text -> Either (ParseErrorBundle Text Void) Int
part2 input = do
robots <- parse parser "" input
pure . snd . minimum $
[ (Down $ maximum $ map length verticalLines, t)
| t <- [0 .. lcm width height - 1],
let verticalLines =
groupConsecutiveBy isLine . Set.toList . Set.fromList $
[ ((y0 + vy * t) `mod` height, (x0 + vx * t) `mod` width)
| ((x0, y0), (vx, vy)) <- robots
]
isLine (y0, x0) (y1, x1) = y0 == y1 && x0 + 1 == x1
]
let (_, bestTime) =
minimum
[ (Down $ maximum $ map length verticalLines, t)
| t <- [0 .. lcm width height - 1],
let verticalLines =
groupConsecutiveBy isLine . Set.toList . Set.fromList $
[ ((y0 + vy * t) `mod` height, (x0 + vx * t) `mod` width)
| ((x0, y0), (vx, vy)) <- robots
]
isLine (y0, x0) (y1, x1) = y0 == y1 && x0 + 1 == x1
]
positions =
Map.fromListWith (+) $
[ (((x0 + vx * bestTime) `mod` width, (y0 + vy * bestTime) `mod` height), 1)
| ((x0, y0), (vx, vy)) <- robots
]
line y =
[ case Map.findWithDefault 0 (x, y) positions of
0 -> '.'
n -> if n < 10 then intToDigit n else '+'
| x <- [0 .. width - 1]
]
mapM_ (traceM . line) [0 .. height - 1]
pure bestTime
where
width = 101
height = 103
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