Day05 yay

--

-- see: https://github.com/sol/hpack

--

-- hash: a31d69558fb7c391bf70ef12c046d4b4a10a2fd42e24f572cc4592799a825b1b

-- hash: 7f535108a3ad03db9bb5b3d1976f1e0422bbe0eddd7da2483c1581fa3dd7c089

name:           advent-of-code

version:        0.0.0

      Day02

      Day03

      Day04

      Day05

      Paths_advent_of_code

  hs-source-dirs:

      src

module Day05 (part1, part2) where

import Data.Char

-- Reduces the input and returns the length.

part1 :: [String] -> String

part1 [input] = show $ length $ reduce input

-- Reduces the input once with every character removed and returns the length of the shortest reduct.

part2 :: [String] -> String

part2 [input] = show $ minBySnd $ liftSnd length <$> liftSnd reduce <$> listRemoves input

example :: [String]

example = ["dabAcCaCBAcCcaDA"]

-- Reduces a list of characters recursively.

reduce :: [Char] -> [Char]

reduce [] = []

reduce (c:cs) = case reduce cs of

    (d:ds) | c `react` d -> ds

           | otherwise -> (c:d:ds)

    [] -> [c]

-- Checks whether two units can react, i.e. are the same character in different cases.

react :: Char -> Char -> Bool

react c1 c2 = c1 /= c2 && toLower c1 == toLower c2

-- Returns a list which contains a pair for each character from 'a' to 'z' with the character and the given string with all occurences (ignoring case) of that character removed.

listRemoves :: String -> [(Char, String)]

listRemoves str = [(c, filter ((/=c) . toLower) str) | c <- ['a'..'z']]

-- Lifts a function to a function working on the second component of a pair.

liftSnd :: (a -> b) -> (c,a) -> (c,b)

liftSnd f (c,a) = (c, f a)

-- Gets the pair with the minimal value in the second component from a list.

minBySnd :: (Ord b) => [(a,b)] -> (a,b)

minBySnd [(a,b)] = (a,b)

minBySnd ((a,b):ls)

    | snd (minBySnd ls) < b = minBySnd ls

    | otherwise = (a,b)

import Day02

import Day03

import Day04

import Day05

solutions :: [((String, String), [String] -> String)]

    (("03", "1"), Day03.part1),

    (("03", "2"), Day03.part2),

    (("04", "1"), Day04.part1),

    (("04", "2"), Day04.part2)]

    (("04", "2"), Day04.part2),

    (("05", "1"), Day05.part1),

    (("05", "2"), Day05.part2)]

main :: IO ()

main = do