aoc-2020-day7

p1.hs

{-# LANGUAGE OverloadedStrings #-}

module Main where

import qualified Data.Map.Strict as M
import qualified Data.Set as S
import Data.List (foldl')
import qualified Data.Text as T
import qualified Data.Text.IO as TIO
import Data.Bifunctor

parseLine :: T.Text -> (T.Text, [(Int, T.Text)])
parseLine raw =
  case T.splitOn " contain " $ T.dropEnd 1 $ T.replace "bag" "" $ T.replace "bags" "" raw of
    [bigger, smallerRaw] | smallerRaw == "no other " -> (T.strip bigger, [])
    [bigger, smallerRaw] ->
      (
        T.strip bigger,
        map parseBagsWithCount $ T.splitOn ", " smallerRaw
      )

  where
    parseBagsWithCount =
      bimap (read . T.unpack) T.strip . T.breakOn " "

-- I anticipate needing a graph the other way for part 2
toGraphs = go M.empty M.empty
  where
    go contains containedBy [] = (contains, containedBy)
    go contains containedBy ((bigger, smaller):rest) =
      go (M.insert bigger smaller contains) (insertContainedBy bigger containedBy smaller) rest

    insertContainedBy = foldl' . consInsert

    consInsert bigger g (_, smaller) | M.member smaller g = M.adjust (bigger :) smaller g
    consInsert bigger g (_, smaller) = M.insert smaller [bigger] g

canContainShinyGold g = go S.empty ["shiny gold"]
  where
    go seen [] = seen
    go seen (current:rest) =
      case M.lookup current g of
        Nothing -> go seen rest
        Just ns ->
          let
            next = filter (`S.notMember` seen) ns
          in
            go (S.union seen (S.fromList next)) (next ++ rest)

main = do
  text <- T.splitOn "\n" . T.strip <$> TIO.readFile "./d7.txt"
  print $ S.size $ canContainShinyGold $ snd $ toGraphs $ map parseLine text

p2.hs

{-# LANGUAGE OverloadedStrings #-}

module Main where

import qualified Data.Map.Strict as M
import Data.List (foldl')
import qualified Data.Text as T
import qualified Data.Text.IO as TIO
import Data.Bifunctor

parseLine :: T.Text -> (T.Text, [(Int, T.Text)])
parseLine raw =
  case T.splitOn " contain " $ T.dropEnd 1 $ T.replace "bag" "" $ T.replace "bags" "" raw of
    [bigger, smallerRaw] | smallerRaw == "no other " -> (T.strip bigger, [])
    [bigger, smallerRaw] ->
      (
        T.strip bigger,
        map parseBagsWithCount $ T.splitOn ", " smallerRaw
      )

  where
    parseBagsWithCount =
      bimap (read . T.unpack) T.strip . T.breakOn " "

toGraphs = go M.empty M.empty
  where
    go contains containedBy [] = (contains, containedBy)
    go contains containedBy ((bigger, smaller):rest) =
      go (M.insert bigger smaller contains) (insertContainedBy bigger containedBy smaller) rest

    insertContainedBy = foldl' . consInsert

    consInsert bigger g (_, smaller) | M.member smaller g = M.adjust (bigger :) smaller g
    consInsert bigger g (_, smaller) = M.insert smaller [bigger] g

neededBags bags g =
  sum [amount + amount*(neededBags (M.findWithDefault [] bag g) g) | (amount, bag) <- bags]

solve g = neededBags (g M.! "shiny gold") g

main = do
  text <- T.splitOn "\n" . T.strip <$> TIO.readFile "./d7.txt"
  print $ solve $ fst $ toGraphs $ map parseLine text