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๐Ÿ‘ช - 2025 DAY 7 SOLUTIONS - ๐Ÿ‘ช (programming.dev)
submitted 10 months ago by [M] to c/advent_of_code@programming.dev
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Day 7: Laboratories

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FAQ

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[โ€“] 4 points 10 months ago* (last edited 10 months ago) (1 child)

Haskell

That was a fun little problem.

import Data.Map qualified as Map  
import Data.Set qualified as Set  
import Data.Tuple (swap)  

readInput s =  
  Map.fromDistinctAscList  
    [((i, j), c) | (i, l) <- zip [0 ..] $ lines s, (j, c) <- zip [0 ..] l]  

beamPaths input = scanl step (Map.singleton startX 1) [startY .. endY]  
  where  
    Just (startY, startX) = lookup 'S' $ map swap $ Map.assocs input  
    Just ((endY, _), _) = Map.lookupMax input  
    step beams y =  
      Map.unionsWith (+) $  
        [ if input Map.!? (y + 1, j) == Just '^'  
            then Map.fromList [(j - 1, n), (j + 1, n)]  
            else Map.singleton j n  
          | (j, n) <- Map.assocs beams  
        ]  

part1 = sum . map Set.size . (zipWith (Set.\\) <*> tail) . map Map.keysSet . beamPaths  

part2 = sum . last . beamPaths  

main = do  
  input <- readInput <$> readFile "input07"  
  print $ part1 input  
  print $ part2 input
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  • [โ€“] 1 point 10 months ago*

    And here's a super-simple version, because why not.

    import Data.List (elemIndex, elemIndices)  
import Data.Map qualified as Map  
import Data.Maybe (fromJust)  
import Data.Set qualified as Set  

main = do  
  (start : rows) <- lines <$> readFile "input07"  
  let splitsByRow =  
        zipWith  
          ( \row beams ->  
              Set.intersection (Map.keysSet beams)  
                . Set.fromDistinctAscList  
                $ elemIndices '^' row  
          )  
          rows  
          beamsByRow  
      beamsByRow =  
        scanl  
          ( \beams splits ->  
              let unsplit = beams `Map.withoutKeys` splits  
                  split = beams `Map.restrictKeys` splits  
                  splitLeft = Map.mapKeysMonotonic pred split  
                  splitRight = Map.mapKeysMonotonic succ split  
               in Map.unionsWith (+) [unsplit, splitLeft, splitRight]  
          )  
          (Map.singleton (fromJust $ elemIndex 'S' start) 1)  
          splitsByRow  
  print . sum $ map Set.size splitsByRow  
  print . sum $ last beamsByRow
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