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2023 day 13

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Star 2 is the most scuffed and probably incorrect thing ever but it produced the
right answer for my input and that's good enough for me.
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eriedaberrie 2023-12-15 23:11:22 -08:00
parent fc5af8bb0b
commit f52cd41da1
2 changed files with 73 additions and 0 deletions
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import Data.List.Split (splitOn)
import Data.List (foldl', transpose)
import qualified Data.Vector.Unboxed as VU
import Data.Vector.Unboxed (Vector)
hashChar :: Char -> Int
hashChar '#' = 1
hashChar '.' = 0
lineToInt :: String -> Int
lineToInt = foldl' (\x y -> 2 * x + hashChar y) 0
matchesAt :: Vector Int -> Int -> Bool
matchesAt v i = VU.reverse rightSide == leftSide
where
nMirrored = min i $ VU.length v - i
leftSide = VU.slice (i - nMirrored) nMirrored v
rightSide = VU.slice i nMirrored v
findMatches :: Vector Int -> [Int]
findMatches v = filter (matchesAt v) [1 .. VU.length v - 1]
solveDirection :: [String] -> Int
solveDirection = sum . findMatches . VU.fromList . map lineToInt
solve :: [String] -> Int
solve l = 100 * solveDirection l + (solveDirection . transpose) l
main :: IO ()
main = print . sum . map (solve . lines) . splitOn "\n\n"
=<< readFile "data.txt"

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import Data.Bits ((.&.), countTrailingZeros, xor)
import Data.List.Split (splitOn)
import Data.List (foldl', transpose)
import qualified Data.Vector.Unboxed as VU
import Data.Vector.Unboxed (Vector)
isPowTwo :: Int -> Bool
isPowTwo n = n .&. (n - 1) == 0
hashChar :: Char -> Int
hashChar '#' = 1
hashChar '.' = 0
lineToInt :: String -> Int
lineToInt = foldl' (\x y -> 2 * x + hashChar y) 0
matchesAt :: Vector Int -> Int -> Bool
matchesAt v i = VU.length differences == 1 && isPowTwo (VU.head differences)
where
nMirrored = min i $ VU.length v - i
leftSide = VU.slice (i - nMirrored) nMirrored v
rightSide = VU.slice i nMirrored v
differences = VU.filter (/= 0)
$ VU.zipWith xor (VU.reverse rightSide) leftSide
findMatches :: Vector Int -> [Int]
findMatches v = filter (matchesAt v) [1 .. VU.length v - 1]
solveDirection :: [String] -> Int
solveDirection = last . (0:) . findMatches . VU.fromList . map lineToInt
solve :: [String] -> Int
solve l = 100 * solveDirection l + (solveDirection . transpose) l
main :: IO ()
main = print . sum . map (solve . lines) . splitOn "\n\n"
=<< readFile "data.txt"