From ac45449f8882a76612dcca699f84f54f08edcff4 Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom.smeding@gmail.com>
Date: Wed, 16 Dec 2020 18:45:47 +0100
Subject: Day 12

---
 2020/12.hs | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/2020/12.hs b/2020/12.hs
index 92ce67c..cb1b1f1 100644
--- a/2020/12.hs
+++ b/2020/12.hs
@@ -72,7 +72,37 @@ sail (Sail offset dirm posm) (State pos dir) =
 manhattan :: Num a => V2 a -> a
 manhattan (V2 a b) = abs a + abs b
 
+------------
+-- PART 2 --
+------------
+
+data State2 = State2 { sPos2 :: V2 Int, sWP :: V2 Int }
+  deriving (Show)
+
+runInstr2 :: String -> State2 -> State2
+runInstr2 (c : ns) = case (c, read ns :: Int) of
+    ('N', n) -> addWP (V2 0 n)
+    ('S', n) -> addWP (V2 0 (-n))
+    ('E', n) -> addWP (V2 n 0)
+    ('W', n) -> addWP (V2 (-n) 0)
+    ('F', n) -> \(State2 ship wp) -> State2 (ship !+! (wp *$ n)) wp
+    ('R', 90) -> mulWP rotRightMat
+    ('R', 180) -> mulWP mirrorMat
+    ('R', 270) -> mulWP rotLeftMat
+    ('L', 90) -> mulWP rotLeftMat
+    ('L', 180) -> mulWP mirrorMat
+    ('L', 270) -> mulWP rotRightMat
+    _ -> error "Cannot parse instr"
+  where
+    rotRightMat = M2 0 1 (-1) 0
+    rotLeftMat = rotRightMat *$ (-1)
+    mirrorMat = M2 (-1) 0 0 (-1)
+    addWP v (State2 ship wp) = State2 ship (wp !+! v)
+    mulWP m (State2 ship wp) = State2 ship (m *! wp)
+runInstr2 _ = error "Cannot parse empty instr"
+
 main :: IO ()
 main = do
-    input <- map parseInstr <$> getInput 12
-    print (manhattan . sPos $ foldl' (flip sail) (State (V2 0 0) (V2 1 0)) input)
+    input <- getInput 12
+    print (manhattan . sPos $ foldl' (flip sail) (State (V2 0 0) (V2 1 0)) (map parseInstr input))
+    print (manhattan . sPos2 $ foldl' (flip runInstr2) (State2 (V2 0 0) (V2 10 1)) input)
-- 
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