1 files changed, 45 insertions, 0 deletions
diff --git a/2020/13a.hs b/2020/13a.hs
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+module Day13A where
+
+import System.Environment (getArgs)
+import Data.Maybe (catMaybes)
+import Data.List.Split (splitOn)
+import Text.Read (readMaybe)
+import Text.Printf
+
+-- Get the nearest bus in the list after the given time
+-- Returns (time, bus)
+getNearest :: Int -> [Int] -> (Int, Int)
+getNearest e xs | not $ null rs = (e, head rs)
+                | otherwise = getNearest (e + 1) xs
+                  where rs = filter (\x -> e `mod` x == 0) xs
+
+-- Parse the input as a string
+-- Returns (current time, list of valid buses)
+parseInput :: String -> (Int, [Int])
+parseInput x = (read t, catMaybes ts)
+              where (t:r) = lines x
+                    bs = splitOn "," (head r)
+                    ts :: [Maybe Int]
+                    ts = map readMaybe bs
+
+-- Parse a file given the path
+-- Returns (current time, list of valid buses)
+parseFromFile :: String -> IO (Int, [Int])
+parseFromFile s = do 
+                   contents <- readFile s;
+                   return $ parseInput contents;
+
+-- runghc --ghc-arg='-package split' 13a.hs inputs/day13
+main :: IO ()
+main = do 
+        args <- getArgs;
+        (now, bs) <- parseFromFile (head args);
+
+        let (t, b) = getNearest now bs;
+        let w = t - now;
+
+        printf "You could get bus %d at %d\n" b t :: IO ();
+        printf "This is a %d minute wait\n" w :: IO ();
+        printf "Answer = %d\n" (b * w) :: IO ();
+
+        return ();