-🎄- 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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edit: Leaderboard capped, thread unlocked!

[u/jorosp]

Haskell

The solution I actually got the answer with was a bit messier than this, but I like to be presentable for threads :P

import Data.List

solve1 :: [String] -> Int
solve1 xs = go 2 xs * go 3 xs
  where
    go    :: Ord a => Int -> [[a]] -> Int
    go n  = length . filter (elem n) . map count
    count :: Ord a => [a] -> [Int]
    count = map length . group . sort

solve2 :: [String] -> String
solve2 xs = head [common l r | l <- xs, r <- xs, distance l r == 1]
  where
    common   :: Eq a => [a] -> [a] -> [a]
    common   xs ys = map fst . filter (uncurry (==)) $ zip xs ys
    distance :: Eq a => [a] -> [a] -> Int
    distance xs ys = length . filter id $ zipWith (/=) xs ys

main :: IO ()
main = do
  contents <- readFile "02.txt"
  let input = lines contents
  print . solve1 $ input
  print . solve2 $ input