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https://github.com/bertptrs/adventofcode.git
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68 lines
2.0 KiB
Haskell
68 lines
2.0 KiB
Haskell
import Data.Array
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import Data.List
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import Data.Maybe
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import Data.Set
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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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initial = Data.Set.singleton startingPoint
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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 = Data.Set.singleton 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 = Data.Set.fromList $ concatMap (checkHit arr) (Data.Set.toList active)
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hits = length (Data.Set.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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