adventofcode-2020/day6/main.hs

#! /usr/bin/env -S"ANSWER=42" nix-shell
#! nix-shell -p ghcid
#! nix-shell -p "haskellPackages.ghcWithPackages (p: with p; [shower])"
#! nix-shell -i "ghcid -c 'ghci -Wall' -T main"

{-# LANGUAGE OverloadedStrings #-}

-- import Debug.Trace (trace)
import Data.List (nub)

exampleData :: [String]
exampleData =
  [ "abc"
  , ""
  , "a"
  , "b"
  , "c"
  , ""
  , "ab"
  , "ac"
  , ""
  , "a"
  , "a"
  , "a"
  , "a"
  , ""
  , "b"
  ]

-- Count how many different chars per paragraph and sum them
countUniqueAnswers :: [String] -> Int
countUniqueAnswers = length . nub . concat

paragraphs :: [String] -> [[String]]
paragraphs strs = go (strs, [])
  where
    go :: ([String], [[String]]) -> [[String]]
    go ([], ys) = ys
    go (x:xs, []) = go (xs, [x] : [])
    go ("":xs, ys) = go (xs, [] : ys)
    go (x:xs, y:ys) = go (xs, (x:y) : ys)

solvePart1 :: [String] -> Int
solvePart1 = sum . (map countUniqueAnswers) . paragraphs

allAnsweredX :: Char -> [[String]] -> [Bool]
allAnsweredX c = map (all (any (== c)))



solvePart2 :: [String] -> Int
solvePart2 strs = length . (filter (== True)) $ concat $ map (\x -> (allAnsweredX x . paragraphs) strs) ['a'..'z']

main :: IO ()
main = do
  putStrLn "Day 6 - Part 1"
  print $ exampleData
  print $ countUniqueAnswers [""]
  print $ countUniqueAnswers ["abc"]
  print $ countUniqueAnswers ["a", "b", "c"]
  print $ countUniqueAnswers ["ab", "ac"]
  putStrLn "Day 6 - Part 1 : solving test"
  print $ solvePart1 exampleData
  putStrLn "Day 6 - Part 1 : solving input"
  input <- lines <$> readFile "day6/input"
  print $ solvePart1 input
  putStrLn "Day 6 - Part 2 : solving test"
  print $ paragraphs exampleData
  print $ solvePart2 exampleData
  putStrLn "Day 6 - Part 2 : solving input"
  print $ solvePart2 input