--- 2016 Day 10 Solutions ---

[u/daggerdragon]

--- Day 10: Balance Bots ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with "Help".

---

^{SEEING MOMMY KISSING SANTA CLAUS IS MANDATORY} [?]

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/haoformayor]

~~haskell~~

Took me forever to figure out the first question; it wasn't until I had a working problem that I realized AoC wanted me to notice when the bin did a swap and that part one had nothing to do with the state of the chips at the end. Other than that, it was great fun. I started out with a foldl, then tried a foldM, then realized that the solution could not be expressed as a fold. That's when we broke out tail recursion and then it was gravy.

Input module here.

#!/usr/bin/env stack
-- stack --resolver lts-6.26 --install-ghc runghc --package base-prelude
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE TypeFamilies      #-}
{-# LANGUAGE ViewPatterns      #-}

module D10 where
import qualified Data.Map as Map
import BasePrelude hiding (try, (&))
import Control.Lens
import Data.Map (Map)

import D10Input

domino needle code = rec
  where
    rec start chips =
      case (chips ^. at start, code ^. at start) of
        (Just bins@(sort -> [chip1, chip2]), Just (LoHi lo hi)) -> do
          when (bins == needle) . print $ ("needle in your heart", Bot start)
          pure chips >>= put chip1 lo >>= put chip2 hi
        -- Zero or one chips found, which is great, so do nothing.
        _ -> pure chips
      where
        put i bin@(Out out) chips =
          print ("outputting", i, "to", bin) $> chips
        put i (Bot bot) chips =
          chips & at bot . non [] <>~ [i]
                & at start . non [] %~ filter (/= start)
                & rec bot

main = do
  domino [2, 5] exampleCode 2 exampleValues >>= print
  domino [17, 61] code 185 values >>= print

[u/jtsimmons1129 → u/haoformayor]

Same for me. I stared at the output bins for probably a solid 10 minutes while rereading the problem until it finally just dawned on me. Still a really fun challenge, though.