Day 19 - Linen Layout

Megathread guidelines

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FAQ

  • @VegOwOtenksEnglish
    2•3 hours ago

    Haskell

    I had several strategy switches from brute-force to pathfinding (when doing part1 input instead of example) because It simply wouldn’t finish. My solution only found the first path to the design, which is why I rewrote to only count how many towels there are for each prefix I have already built. Do that until there is either only one entry with the total combinations count or no entry and it’s impossible to build the design.

    I like the final solution, its small (unlike my other solutions) and runs fast.

    🚀 
    import Control.Arrow

import Data.Map (Map)

import qualified Data.List as List
import qualified Data.Map as Map

parse :: String -> ([String], [String])
parse = lines . init
        >>> (map (takeWhile (/= ',')) . words . head &&& drop 2)

countDesignPaths :: [String] -> String -> Map Int Int -> Int
countDesignPaths ts d es
        | Map.null es    = 0
        | ml == length d = mc
        | otherwise = countDesignPaths ts d es''
        where
                ((ml, mc), es') = Map.deleteFindMin es
                ns = List.filter (flip List.isPrefixOf (List.drop ml d))
                        >>> List.map length
                        >>> List.map (ml +)
                        $ ts
                es'' = List.foldl (\ m l' -> Map.insertWith (+) l' mc m) es'
                        $ ns
solve (ts, ds) = List.map (flip (countDesignPaths ts) (Map.singleton 0 1))
        >>> (List.length . List.filter (/= 0) &&& List.sum)
        $ ds

main = getContents
        >>= print
        . solve
        . parse