1 files changed, 67 insertions, 0 deletions
diff --git a/2020/12b.hs b/2020/12b.hs
new file mode 100644
index 0000000..040287e
--- /dev/null
+++ b/2020/12b.hs
@@ -0,0 +1,67 @@
+module Day12B where
+
+import System.Environment (getArgs)
+
+data Instruction = North Int | East Int |
+                   South Int | West Int |
+                   TLeft Int | TRight Int |
+                   Forward Int
+                deriving (Eq, Show, Ord);
+
+-- ((shipX, shipY), (wY, wX))
+type State = ((Int, Int), (Int, Int));
+
+initialState :: State;
+initialState = ((0, 0), (10, 1));
+
+rotateAround :: (Int, Int) -> Int -> (Int, Int)
+rotateAround (wx, wy) (-90) = (-wy, wx)
+rotateAround (wx, wy) 0 = (wx, wy)
+rotateAround (wx, wy) 90 = (wy, -wx)
+rotateAround (wx, wy) 180 = (-wx, -wy)
+rotateAround (wx, wy) (-180) = rotateAround (wx, wy) 180
+rotateAround (wx, wy) 270 = rotateAround (wx, wy) (-90)
+rotateAround (wx, wy) (-270) = rotateAround (wx, wy) 90
+rotateAround _ _ = error "Direction not defined"
+
+moveToward :: (Int, Int) -> (Int, Int) -> Int -> (Int, Int)
+moveToward (sx, sy) (wx, wy) r = (sx + (wx * r), sy + (wy * r))
+
+readInstructions :: String -> [Instruction]
+readInstructions = map readInstruction . lines
+            where readInstruction ('N':xs) = North $ read xs
+                  readInstruction ('S':xs) = South $ read xs
+                  readInstruction ('E':xs) = East $ read xs
+                  readInstruction ('W':xs) = West $ read xs
+                  readInstruction ('L':xs) = TLeft $ read xs
+                  readInstruction ('R':xs) = TRight $ read xs
+                  readInstruction ('F':xs) = Forward $ read xs
+                  readInstruction _ = error "Invalid instruction"
+
+doInstruction :: Instruction -> State -> State
+doInstruction (North r) ((sx, sy), (wx, wy)) = ((sx, sy), (wx, wy + r))
+doInstruction (South r) ((sx, sy), (wx, wy)) = ((sx, sy), (wx, wy - r))
+doInstruction (East r) ((sx, sy), (wx, wy)) = ((sx, sy), (wx + r, wy))
+doInstruction (West r) ((sx, sy), (wx, wy)) = ((sx, sy), (wx - r, wy))
+doInstruction (TLeft r) ((sx, sy), (wx, wy)) = ((sx, sy), rotateAround (wx, wy) (-r))
+doInstruction (TRight r) ((sx, sy), (wx, wy)) = ((sx, sy), rotateAround (wx, wy) r)
+doInstruction (Forward r) ((sx, sy), (wx, wy)) = (moveToward (sx, sy) (wx, wy) r, (wx, wy))
+
+instructionsFromFile :: String -> IO [Instruction]
+instructionsFromFile s = do 
+                   contents <- readFile s;
+                   return $ readInstructions contents;
+
+main :: IO ()
+main = do 
+        args <- getArgs;
+        is <- instructionsFromFile (head args);
+
+        let final = foldl (flip doInstruction) initialState is;
+        putStrLn $ "Final State: " ++ show final;
+
+        let ((x, y), _) = final;
+        let dist = abs x + abs y;
+        putStrLn $ "Distance: " ++ show dist;
+
+        return ();