Part 1

day13/main.hs

@@ -5,7 +5,7 @@
 
 {-# OPTIONS_GHC -Wall -Wincomplete-uni-patterns #-}
 {-# OPTIONS_GHC -Wno-unused-top-binds -Wno-unused-imports #-}
-{-# OPTIONS_GHC -Wno-unused-matches #-}
+{-# OPTIONS_GHC -Wno-unused-matches -Wno-type-defaults #-}
 {-# LANGUAGE OverloadedStrings #-}
 
 import Control.Applicative
@@ -13,27 +13,41 @@ import Data.Attoparsec.Text (Parser)
 import Data.Text (Text)
 import Debug.Trace (trace)
 import Text.Pretty.Simple
+import Data.Maybe (fromMaybe,catMaybes)
+import Data.List (find,sortOn)
 import qualified Data.Attoparsec.Text as A
 import qualified Data.Text as T
 
 exampleData :: String
 exampleData = "939\n7,13,x,x,59,x,31,19"
 
-numOrXParser :: Parser Text
-numOrXParser = A.takeWhile (/= ',')
+numOrXParser :: Parser (Maybe Int)
+numOrXParser = (Just <$> A.decimal) <|> ("x" *> pure Nothing)
 
 inputParser :: Parser (Int,[Int])
 inputParser = do
   n <- A.decimal
   A.skipSpace
   xs <- numOrXParser `A.sepBy` ","
-  pure (n,read <$> T.filter (/= ',') xs)
+  pure (n,catMaybes $ xs)
 
 parseInput :: String -> Either String (Int,[Int])
 parseInput = (A.parseOnly inputParser) . T.pack
 
+solvePart1 :: String -> Either String Int
+solvePart1 str = do
+  (n,xs) <- parseInput str
+  let (bus, time) = head
+                  $ sortOn (snd)
+                  $ map (\x -> (x,fromMaybe (-1) $ find (> n) [0,x..])) xs
+  pure $ bus * (time - n)
+
 main :: IO ()
 main = do
   putStrLn ":: Test"
-  A.parseTest inputParser $ T.pack exampleData
+  pPrint $ A.parseOnly inputParser $ T.pack exampleData
+  pPrint $ take 3 ((\n -> [1,n..]) 59)
   putStrLn ":: Day 13 - Part 1"
+  input <- readFile "day13/input"
+  pPrint $ solvePart1 exampleData
+  pPrint $ solvePart1 input