Working Day 1 (1 + 2)

day1/Main.hs

@@ -2,13 +2,43 @@
 
 module Main where
 
+import Data.Char (digitToInt)
+import Data.Text (strip, pack, unpack)
 import Paths_aoc2017
+import System.Environment (getArgs)
+import System.Exit (exitSuccess)
 
 file :: IO FilePath
 file = getDataFileName "data/1-1"
 
-getData :: IO String
-getData = readFile =<< file
+getData :: IO [Int]
+getData = map digitToInt . unpack . strip . pack <$> (readFile =<< file)
+
+rotate :: Int -> [Int] -> [Int]
+rotate _ [] = []
+rotate n xs = drop n xs ++ take n xs
+
+formPairs :: Int -> [Int] -> [(Int, Int)]
+formPairs n l = zip l $ rotate n l
+
+usage :: IO ()
+usage = putStrLn "Usage: stack exec day-n [--two] [...args]"
+
+doOne :: [String] -> IO ()
+doOne _ = print . sum . map fst . filter (uncurry (==)) <$> formPairs 1 =<< getData
+
+doTwo :: [String] -> IO ()
+doTwo _ =
+  print . sum . map fst . filter (uncurry (==)) <$> (\l -> formPairs (length l `div` 2) l) =<<
+  getData
+
+parse :: [String] -> IO ()
+parse ("--two":xs) = doTwo xs
+parse ["--help"] = usage
+parse xs = doOne xs
 
 main :: IO ()
-main = print =<< getData
+main = do
+  args <- getArgs
+  parse args
+  exitSuccess

package.yaml

@@ -15,6 +15,7 @@ extra-source-files:
 
 dependencies:
 - base >=4.7 && <5
+- text >=1.2.2.0
 ghc-options: [-Wall, -Wwarn]
 
 library: