2020-13 in haskell

This commit is contained in:
Julien Dessaux 2023-03-24 01:17:50 +01:00
parent ff9f5d5045
commit 99dcde4240
Signed by: adyxax
GPG key ID: F92E51B86E07177E
4 changed files with 134 additions and 0 deletions

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-- requires cabal install --lib megaparsec parser-combinators
module Main (main) where
import Control.Monad (void, when)
import Data.List (elemIndex)
import Data.Maybe (catMaybes, fromJust)
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
import System.Exit (die)
exampleExpectedOutput = 295
type Input = (Int, [Maybe Int])
type Parser = Parsec Void String
parseShuttle :: Parser (Maybe Int)
parseShuttle = do
num <- (Just . read <$> some digitChar) <|> (char 'x' *> return Nothing)
void . optional $ char ','
return $ num
parseOps :: Parser Input
parseOps = do
time <- some digitChar
void $ char '\n'
shuttles <- some parseShuttle
void $ char '\n'
void $ eof
return $ ((read time), shuttles)
parseInput :: String -> IO Input
parseInput filename = do
input <- readFile filename
case runParser parseOps filename input of
Left bundle -> die $ errorBundlePretty bundle
Right ops -> return ops
compute :: Input -> Int
compute (time, shuttles) = departure * busId
where
busId = allShuttles !! (fromJust $ elemIndex departure nextDepartures)
departure = minimum nextDepartures
nextDepartures = map (\a -> (-time) `mod` a) allShuttles
allShuttles = catMaybes shuttles
main :: IO ()
main = do
example <- parseInput "example"
let exampleOutput = compute example
when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
input <- parseInput "input"
print $ compute input

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19,x,x,x,x,x,x,x,x,41,x,x,x,37,x,x,x,x,x,821,x,x,x,x,x,x,x,x,x,x,x,x,13,x,x,x,17,x,x,x,x,x,x,x,x,x,x,x,29,x,463,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,23

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-- requires cabal install --lib megaparsec parser-combinators
module Main (main) where
import Control.Monad (void, when, zipWithM)
import Data.Either (fromRight)
import Data.List (foldl')
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
import System.Exit (die)
exampleExpectedOutput = 1068781
type Input = [Maybe Int]
type Parser = Parsec Void String
parseShuttle :: Parser (Maybe Int)
parseShuttle = do
num <- (Just . read <$> some digitChar) <|> (char 'x' *> return Nothing)
void . optional $ char ','
return $ num
parseOps :: Parser Input
parseOps = do
void $ some digitChar
void $ char '\n'
shuttles <- some parseShuttle
void $ char '\n'
void $ eof
return $ shuttles
parseInput :: String -> IO Input
parseInput filename = do
input <- readFile filename
case runParser parseOps filename input of
Left bundle -> die $ errorBundlePretty bundle
Right ops -> return ops
-- From rosetta code https://rosettacode.org/wiki/Chinese_remainder_theorem#Haskell
egcd :: Int -> Int -> (Int, Int)
egcd _ 0 = (1, 0)
egcd a b = (t, s - q * t)
where
(s, t) = egcd b r
(q, r) = a `quotRem` b
modInv :: Int -> Int -> Either String Int
modInv a b =
case egcd a b of
(x, y)
| a * x + b * y == 1 -> Right x
| otherwise ->
Left $ "No modular inverse for " ++ show a ++ " and " ++ show b
chineseRemainder :: [Int] -> [Int] -> Either String Int
chineseRemainder residues modulii =
zipWithM modInv crtModulii modulii >>=
(Right . (`mod` modPI) . sum . zipWith (*) crtModulii . zipWith (*) residues)
where
modPI = product modulii
crtModulii = (modPI `div`) <$> modulii
-- end of snippet from rosetta code
compute :: Input -> Int
compute input = fromRight 0 . uncurry chineseRemainder $ unzip $ fst $ foldl' accumul ([], 0) input
where
accumul :: ([(Int, Int)], Int) -> Maybe Int -> ([(Int, Int)], Int)
accumul (acc, i) Nothing = (acc, i+1)
accumul (acc, i) (Just v) = (acc ++ [(-i, v)], i+1)
main :: IO ()
main = do
example <- parseInput "example"
let exampleOutput = compute example
when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
input <- parseInput "input"
print $ compute input