diff --git a/cis194/week12/stevemao/Risk.hs b/cis194/week12/stevemao/Risk.hs
new file mode 100644
index 00000000..abbd4fe2
--- /dev/null
+++ b/cis194/week12/stevemao/Risk.hs
@@ -0,0 +1,118 @@
+{-# OPTIONS_GHC -Wall #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+
+module Risk where
+
+import Control.Monad.Random
+import Data.List
+import Data.Universe.Helpers
+import Data.Tree
+import Data.Bifunctor
+import Debug.Trace
+
+------------------------------------------------------------
+-- Die values
+
+newtype DieValue = DV { unDV :: Int } 
+  deriving (Eq, Ord, Show, Num, Enum)
+
+-- first :: (a -> b) -> (a, c) -> (b, c)
+-- first f (a, c) = (f a, c)
+
+instance Random DieValue where
+  random           = first DV . randomR (1,6)
+  randomR (low,hi) = first DV . randomR (max 1 (unDV low), min 6 (unDV hi))
+
+die :: Rand StdGen DieValue
+die = getRandom
+
+------------------------------------------------------------
+-- Risk
+
+type Army = Int
+
+data Battlefield = Battlefield { attackers :: Army, defenders :: Army }
+  deriving Show
+
+sortReverse :: Functor f => f [DieValue] -> f [DieValue]
+sortReverse = fmap $ reverse . sort
+
+dieMany :: Int -> Rand StdGen [DieValue]
+dieMany n = sortReverse . replicateM n $ die
+
+cartprod :: [[a]] -> [[a]];
+cartprod [] = [[]]
+cartprod (xs:xss) = [x:ys | x<- xs, ys <-yss]
+                        where yss = cartprod xss
+
+diePlanned :: Int -> [[DieValue]]
+diePlanned n = sortReverse . cartprod . replicate n $ [1..6]
+
+count   :: Eq a => a -> [a] -> Int
+count x =  length . filter (==x)
+
+countSnd :: Eq a => a -> [(b, a)] -> Int
+countSnd x = count x . fmap snd
+
+battle' :: Monad m => (Int -> m [DieValue]) -> Battlefield -> m Battlefield
+battle' m (Battlefield a d) = do 
+  let maxA = min (a - 1) 3
+  let maxD = min d 2
+
+  attacks <- m maxA
+  defends <- m maxD
+
+  let results = zipWith (>) attacks defends
+
+  return . Battlefield (a - count False results) $ d - count True results
+
+battle :: Battlefield -> Rand StdGen Battlefield
+battle = battle' dieMany
+
+battleAll :: Battlefield -> [(Double, Battlefield)]
+battleAll (Battlefield _ 0) = []
+battleAll (Battlefield a d)
+  | a < 2 = []
+  | otherwise = do
+      let maxA = min (a - 1) 3
+      let maxD = min d 2
+
+      let attackss = diePlanned maxA -- [[1,1,1], [2,1,1]...]
+      let defendss = diePlanned maxD -- [[1,1], [2,1]...]
+
+      let allPossibilities = attackss +*+ defendss -- [([1,1,1], [1,1]), ([2,1,1], [1,1])...]
+      let allResults = fmap (uncurry $ zipWith (>)) allPossibilities
+
+      let allResultsWithPercent = foldr (\curr acc -> if countSnd curr acc == 0 then (1, curr) : acc else fmap (\(co, cu) -> if cu == curr then (co + 1, cu) else (co, cu)) acc) [] allResults
+      let allResultsNum = fromIntegral $ length allResults
+      
+      let ret = fmap (bimap (/ allResultsNum) (\r -> Battlefield (a - count False r) $ d - count True r)) allResultsWithPercent
+      trace (show ret) ret
+
+invade :: Battlefield -> Rand StdGen Battlefield
+invade b@(Battlefield _ 0) = pure b
+invade b@(Battlefield a _)
+  | a < 2 = pure b
+  | otherwise = battle b >>= invade
+
+successProb :: Battlefield -> Rand StdGen Double
+successProb = fmap (\bs -> foldr f 0 bs / fromIntegral simCount) . replicateM simCount . invade
+  where f :: Battlefield -> Double -> Double
+        f (Battlefield _ 0) acc = acc + 1
+        f _ acc = acc
+        simCount = 1000 :: Int
+
+buildTree :: Battlefield -> Tree (Double, Battlefield)
+buildTree b = unfoldTree f (1, b)
+  where f :: (Double, Battlefield) -> ((Double, Battlefield), [(Double, Battlefield)])
+        f c@(_, ba) = (c, battleAll ba)
+
+calculateProb :: Tree (Double, Battlefield) -> Double
+calculateProb = foldTree f
+  where f :: (Double, Battlefield) -> [Double] -> Double
+        f (percent, Battlefield _ 0) [] = percent
+        f _ [] = 0
+        f (percent, _) forest = sum . fmap (* percent) $ forest 
+
+exactSuccessProb :: Battlefield -> Double
+exactSuccessProb = calculateProb . buildTree