4 files changed, 934 insertions, 0 deletions

diff --git a/2020/12-Rain_Risk/example b/2020/12-Rain_Risk/example
new file mode 100644
index 0000000..d382291
--- /dev/null
+++ b/2020/12-Rain_Risk/example
@@ -0,0 +1,5 @@
+F10
+N3
+F7
+R90
+F11
diff --git a/2020/12-Rain_Risk/first.hs b/2020/12-Rain_Risk/first.hs
new file mode 100644
index 0000000..e4e204e
--- /dev/null
+++ b/2020/12-Rain_Risk/first.hs
@@ -0,0 +1,89 @@
+-- requires cabal install --lib megaparsec parser-combinators
+module Main (main) where
+import Control.Monad (void, when)
+import Data.List (foldl')
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+import System.Exit (die)
+
+exampleExpectedOutput = 25
+
+data Action = N | S | E | W | L | R | F
+data Heading = HN | HS | HE | HW
+data Op = Op Action Int
+
+type Parser = Parsec Void String
+
+parseOp :: Parser Op
+parseOp = do
+  action <- (char 'N' *> return N)
+        <|> (char 'S' *> return S)
+        <|> (char 'E' *> return E)
+        <|> (char 'W' *> return W)
+        <|> (char 'L' *> return L)
+        <|> (char 'R' *> return R)
+        <|> (char 'F' *> return F)
+  num <- some digitChar
+  void $ char '\n'
+  return $ Op action (read num)
+
+parseOps :: Parser [Op]
+parseOps = some parseOp <* eof
+
+parseInput :: String -> IO [Op]
+parseInput filename = do
+  input <- readFile filename
+  case runParser parseOps filename input of
+    Left bundle -> die $ errorBundlePretty bundle
+    Right ops -> return ops
+
+compute :: [Op]-> Int
+compute ops = (\(x, y, _) -> abs(x)+abs(y)) $ foldl' step (0, 0, HE) ops
+  where
+    step :: (Int, Int, Heading) -> Op -> (Int, Int, Heading)
+    step (x, y, h) (Op N i) = (x, y+i, h)
+    step (x, y, h) (Op S i) = (x, y-i, h)
+    step (x, y, h) (Op E i) = (x+i, y, h)
+    step (x, y, h) (Op W i) = (x-i, y, h)
+    step (x, y, HN) (Op F i) = (x, y+i, HN)
+    step (x, y, HS) (Op F i) = (x, y-i, HS)
+    step (x, y, HE) (Op F i) = (x+i, y, HE)
+    step (x, y, HW) (Op F i) = (x-i, y, HW)
+    step (x, y, h) (Op a i) = (x, y, turn h a i)
+    turn :: Heading -> Action -> Int -> Heading
+    turn h a i = turn' h a mi
+      where mi = (i `mod` 360) `div` 90
+    turn' HN L 1 = HW
+    turn' HN L 2 = HS
+    turn' HN L 3 = HE
+    turn' HS L 1 = HE
+    turn' HS L 2 = HN
+    turn' HS L 3 = HW
+    turn' HE L 1 = HN
+    turn' HE L 2 = HW
+    turn' HE L 3 = HS
+    turn' HW L 1 = HS
+    turn' HW L 2 = HE
+    turn' HW L 3 = HN
+    turn' HN R 1 = HE
+    turn' HN R 2 = HS
+    turn' HN R 3 = HW
+    turn' HS R 1 = HW
+    turn' HS R 2 = HN
+    turn' HS R 3 = HE
+    turn' HE R 1 = HS
+    turn' HE R 2 = HW
+    turn' HE R 3 = HN
+    turn' HW R 1 = HN
+    turn' HW R 2 = HE
+    turn' HW R 3 = HS
+    turn' h _ _ = h
+
+main :: IO ()
+main = do
+  example <- parseInput "example"
+  let exampleOutput = compute example
+  when  (exampleOutput /= exampleExpectedOutput)  (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+  input <- parseInput "input"
+  print $ compute input
diff --git a/2020/12-Rain_Risk/input b/2020/12-Rain_Risk/input
new file mode 100644
index 0000000..ab0ccce
--- /dev/null
+++ b/2020/12-Rain_Risk/input
@@ -0,0 +1,774 @@
+E2
+F24
+F60
+N3
+E1
+R180
+F14
+L90
+N4
+W3
+F81
+R90
+F43
+R90
+F40
+S2
+F56
+L90
+E1
+S1
+R90
+F66
+L180
+W2
+F84
+R90
+E4
+F32
+E5
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+F44
+E1
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+E4
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+N1
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+F86
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diff --git a/2020/12-Rain_Risk/second.hs b/2020/12-Rain_Risk/second.hs
new file mode 100644
index 0000000..c036def
--- /dev/null
+++ b/2020/12-Rain_Risk/second.hs
@@ -0,0 +1,66 @@
+-- requires cabal install --lib megaparsec parser-combinators
+module Main (main) where
+import Control.Monad (void, when)
+import Data.List (foldl')
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+import System.Exit (die)
+
+exampleExpectedOutput = 286
+
+data Action = N | S | E | W | L | R | F
+data Op = Op Action Int
+
+type Parser = Parsec Void String
+
+parseOp :: Parser Op
+parseOp = do
+  action <- (char 'N' *> return N)
+        <|> (char 'S' *> return S)
+        <|> (char 'E' *> return E)
+        <|> (char 'W' *> return W)
+        <|> (char 'L' *> return L)
+        <|> (char 'R' *> return R)
+        <|> (char 'F' *> return F)
+  num <- some digitChar
+  void $ char '\n'
+  return $ Op action (read num)
+
+parseOps :: Parser [Op]
+parseOps = some parseOp <* eof
+
+parseInput :: String -> IO [Op]
+parseInput filename = do
+  input <- readFile filename
+  case runParser parseOps filename input of
+    Left bundle -> die $ errorBundlePretty bundle
+    Right ops -> return ops
+
+compute :: [Op]-> Int
+compute ops = (\((x, y), _) -> abs(x)+abs(y)) $ foldl' step ((0, 0), (10, 1)) ops
+  where
+    step :: ((Int, Int), (Int, Int)) -> Op -> ((Int, Int), (Int, Int))
+    step (p, (wx, wy)) (Op N i) = (p, (wx, wy+i))
+    step (p, (wx, wy)) (Op S i) = (p, (wx, wy-i))
+    step (p, (wx, wy)) (Op E i) = (p, (wx+i, wy))
+    step (p, (wx, wy)) (Op W i) = (p, (wx-i, wy))
+    step ((x, y), (wx, wy)) (Op F i) = ((x+i*wx, y+i*wy), (wx, wy))
+    step (p, w) (Op a i) = (p, turn w a i)
+    turn :: (Int, Int) -> Action -> Int -> (Int, Int)
+    turn w a i = turn' w a mi
+      where mi = (i `mod` 360) `div` 90
+    turn' (wx, wy) L 1 = (-wy, wx)
+    turn' (wx, wy) _ 2 = (-wx, -wy)
+    turn' (wx, wy) L 3 = (wy, -wx)
+    turn' (wx, wy) R 1 = (wy, -wx)
+    turn' (wx, wy) R 3 = (-wy, wx)
+    turn' w _ _ = w
+
+main :: IO ()
+main = do
+  example <- parseInput "example"
+  let exampleOutput = compute example
+  when  (exampleOutput /= exampleExpectedOutput)  (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+  input <- parseInput "input"
+  print $ compute input