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-- requires cabal install --lib megaparsec parser-combinators
module Main (main) where
import Control.Applicative.Permutations
import Control.Monad (void, when)
import Data.Char qualified as C
import Data.Either
import Data.Functor
import Data.List qualified as L
import Data.Map qualified as M
import Data.Maybe
import Data.Set qualified as S
import Data.Vector qualified as V
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
import Debug.Trace
exampleExpectedOutput = 374
type Position = (Int, Int)
type Input = [Position]
type Parser = Parsec Void String
parseLine :: Parser Position
parseLine = do
(SourcePos _ y x) <- getSourcePos
void $ char '#' <* some (void (char '.') <|> void eol)
return (unPos x, unPos y)
parseInput' :: Parser Input
parseInput' = do
some (void (char '.') <|> void eol)
some parseLine <* eof
parseInput :: String -> IO Input
parseInput filename = do
input <- readFile filename
case runParser parseInput' filename input of
Left bundle -> error $ errorBundlePretty bundle
Right input' -> return input'
compute :: Input -> Int
compute input = distances $ map expand input
where
distances :: Input -> Int
distances [] = 0
distances (x:xs) = distances' x xs + distances xs
distances' :: Position -> Input -> Int
distances' a [] = 0
distances' a (x:xs) = distance a x + distances' a xs
distance :: Position -> Position -> Int
distance (x1, y1) (x2, y2) = abs (x2-x1) + abs (y2-y1)
expand :: Position -> Position
expand (x, y) = (x', y')
where
x' = x + S.size (S.filter (< x) emptyCols)
y' = y + S.size (S.filter (< y) emptyRows)
cols = S.fromList $ map fst input
rows = S.fromList $ map snd input
allCols = S.fromList [0..S.findMax cols]
allRows = S.fromList [0..S.findMax rows]
emptyCols = allCols S.\\ cols
emptyRows = allRows S.\\ rows
main :: IO ()
main = do
example <- parseInput "example"
let exampleOutput = compute example
when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
input <- parseInput "input"
print $ compute input
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