e64af48b80
6ef036e2c5a actually made the solution incorrect, the list comprehension
for part b relied on V 0 0 being in the list for the element to match
the step number. The magic oneliner is rad tho so simply adjust the
list comprehension.
35 lines
1015 B
Haskell
35 lines
1015 B
Haskell
import Data.List.Split
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import Data.List
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import qualified Data.Set as Set
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import Data.Maybe
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import Linear.V2
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main = do
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content <- readFile "input"
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let [trace1, trace2] = map gensteps $ parse content
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print (day3a trace1 trace2)
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print (day3b trace1 trace2)
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parse :: String -> [[(Char,Int)]]
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parse = map (map (\x->(head x,read $ tail x))) . map (splitOn ",") . lines
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gensteps :: [(Char,Int)] -> [V2 Int]
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gensteps = scanl1 (+) . concatMap (\(x,y)->replicate y $ step x)
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step :: Char -> V2 Int
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step x
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| x=='U'=V2 0 1
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| x=='R'=V2 1 0
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| x=='D'=V2 0 (-1)
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| x=='L'=V2 (-1) 0
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day3a :: [V2 Int] -> [V2 Int] -> Int
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day3a xs ys = Set.findMin $ Set.map manhattan (intersections xs ys)
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where manhattan (V2 x y) = abs x + abs y
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intersections :: [V2 Int] -> [V2 Int] -> Set.Set (V2 Int)
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intersections xs ys = (Set.fromList xs) `Set.intersection` (Set.fromList ys)
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day3b xs ys = minimum [let f = succ . fromJust . elemIndex x in
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f xs + f ys | x<-Set.toList $ intersections xs ys]
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