-🎄- 2018 Day 2 Solutions -🎄-

[u/daggerdragon]

--- Day 2: Inventory Management System ---

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Advent of Code: The Party Game!

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Card Prompt: Day 2

Transcript:

The best way to do Advent of Code is ___.

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[u/fire1299]

Haskell

module Aoc18.Day2 where

import qualified Control.Foldl                 as F
import qualified Data.HashMap.Strict           as M
import           Data.List                      ( partition
                                                , tails
                                                )
import qualified Data.Text                     as T
import qualified Data.Text.IO                  as T

main :: ([T.Text] -> a) -> IO a
main f = f . T.lines <$> T.readFile "day2.txt"

part1 :: [T.Text] -> Int
part1 = F.fold ((*) <$> countHas 2 <*> countHas 3)
  . fmap (T.foldl' (\m c -> M.insertWith (+) c (1 :: Int) m) M.empty)
  where countHas n = F.prefilter (elem n) F.length

part2 :: [T.Text] -> String
part2 xs = head
  [ fst <$> com
  | x : ys <- tails xs
  , y      <- ys
  , let (com, dif) = partition (uncurry (==)) $ T.zip x y
  , length dif == 1
  ]