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https://github.com/bertptrs/adventofcode.git
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Bert Peters
be6c3d37ea
Avoid repeatedly creating sets that live for almost no time, as well as some readability fixes
66 lines
1.9 KiB
Haskell
66 lines
1.9 KiB
Haskell
import Data.Array
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import Data.List
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import Data.Maybe
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import System.Environment
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import System.Exit
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main = getArgs >>= parse >>= run
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stringToArray :: [Char] -> Array Int Char
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stringToArray s = listArray (0, length s - 1) s
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run :: String -> IO ()
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run input =
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let gridLines = lines input
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startingPoint = findStartingPoint $ head gridLines
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arrLines = Data.List.map stringToArray $ tail gridLines
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in do
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print $ part1 arrLines startingPoint
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print $ part2 arrLines startingPoint
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findStartingPoint :: [Char] -> Int
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findStartingPoint line = fromJust $ elemIndex 'S' line
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part1 arrLines startingPoint =
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let initial = [startingPoint]
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in simulate arrLines 0 initial
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checkHit :: Array Int Char -> Int -> [Int]
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checkHit line idx = case line ! idx of
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'^' -> (idx - 1) : [idx + 1]
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_ -> [idx]
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simulate [] count active = count
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simulate lines count active =
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let arr = head lines
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followUp = nub $ concatMap (checkHit arr) active
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hits = length $ Data.List.filter (\i -> arr ! i == '^') active
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remainder = tail lines
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in simulate remainder (hits + count) followUp
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part2 :: [Array Int Char] -> Int -> Int
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part2 arrLines startingPosition =
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let n = length arrLines
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arr = listArray (0, n - 1) arrLines
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width = length $ head arrLines
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compute i pos
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| i >= n = 1
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| otherwise =
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let line = arr ! i
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in case line ! pos of
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'^' -> memo ! (i + 1, pos - 1) + memo ! (i + 1, pos + 1)
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_ -> memo ! (i + 1, pos)
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memo =
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array
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((0, 0), (n, width - 1))
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[((i, pos), compute i pos) | i <- [0 .. n], pos <- [0 .. width - 1]]
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in memo ! (0, startingPosition)
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parse ["-h"] = usage >> exitSuccess
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parse [] = usage >> die usageStr
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parse fs = concat `fmap` mapM readFile fs
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usageStr = "Usage: solve [-vh] [file ..]"
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usage = putStrLn usageStr
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