81 lines
2.1 KiB
Haskell
Executable file
81 lines
2.1 KiB
Haskell
Executable file
#! /usr/bin/env -S"ANSWER=42" nix-shell
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#! nix-shell -p ghcid
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#! nix-shell -p "haskellPackages.ghcWithPackages (p: with p; [attoparsec])"
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#! nix-shell -i "ghcid -c 'ghci -Wall' -T main"
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{-# LANGUAGE OverloadedStrings #-}
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import Data.Attoparsec.Text
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import Data.Text (pack)
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import Data.Maybe (catMaybes)
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import Data.Bits (xor)
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testData :: [String]
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testData = [ "1-3 a: abcde"
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, "1-3 b: cdefg"
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, "2-9 c: ccccccccc"
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]
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data Input = Input {
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atLeast :: Int
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, notMore :: Int
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, character :: Char
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, password :: String
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} deriving Show
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inputParser :: Parser Input
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inputParser = do
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atLeast' <- decimal
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_ <- char '-'
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notMore' <- decimal
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_ <- space
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character' <- letter
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_ <- char ':'
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_ <- space
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password' <- many1 letter
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return $ Input atLeast' notMore' character' password'
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parseInputLine :: String -> Maybe Input
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parseInputLine s = eitherToMaybe $ parseOnly inputParser (pack s)
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eitherToMaybe :: Either a b -> Maybe b
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eitherToMaybe (Right e) = Just e
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eitherToMaybe (Left _) = Nothing
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-- How many passwords are valid according to their policies?
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validatePassword1 :: Input -> Bool
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validatePassword1 (Input min' max' char' pass) =
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c >= min' && c <= max'
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where
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c = (length . filter (== char')) pass
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-- How many passwords are valid according to the new interpretation of the
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-- policies?
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validatePassword2 :: Input -> Bool
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validatePassword2 (Input pos1 pos2 char' pass) =
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(pass !! (pos1-1) == char') `xor` (pass !! (pos2-1) == char')
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validateLine :: (Input -> Bool) -> String -> Maybe Bool
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validateLine f s = do
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i <- parseInputLine s
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pure $ f i
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countTrue :: [Bool] -> Int
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countTrue = length . filter (== True)
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solveDay2Part1 :: [String] -> Int
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solveDay2Part1 = countTrue . catMaybes . (map (validateLine validatePassword1))
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solveDay2Part2 :: [String] -> Int
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solveDay2Part2 = countTrue . catMaybes . (map (validateLine validatePassword2))
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main :: IO ()
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main = do
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putStrLn "Day 2 - Part 1"
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inputData <- readFile "./day2/input"
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print $ solveDay2Part1 testData
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print $ solveDay2Part1 (lines inputData)
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print $ solveDay2Part2 testData
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print $ solveDay2Part2 (lines inputData)
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