Submission #5417737

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Source Code Expand

import qualified Control.Monad as M
import qualified Data.Map as Map
import qualified Data.List as L
import Data.Maybe (fromJust)

data Turn = Sunuke | Sumeke deriving (Show, Eq, Ord)
type Point = Int
type Stack = ([Int], [Int])
type Game = (Turn, Stack)

main = do
    _ <- getLine
    as <- map read . words <$> getLine
    bs <- map read . words <$> getLine
    print $ evalDP run Map.empty$ (Sunuke, (as, bs))

run :: DP Game Point
run = dp $ \g@(trn, stc) -> do
    memo <- get
    let moves = getMoves stc
    if isEmpty stc
        then return 0
        else if trn == Sunuke
            then return $ maximum [p'+ evalDP run memo (Sumeke, s') | (s', p') <- moves]
            else return $ minimum [0 + evalDP run memo (Sunuke, s') | (s', p') <- moves]

isEmpty :: Stack -> Bool
isEmpty (as, bs) = null as && null bs

getMoves :: Stack -> [(Stack, Point)]
getMoves ([]  , []  ) = []
getMoves (a:as, []  ) = [((as, []), a)]
getMoves ([]  , b:bs) = [(([], bs), b)]
getMoves (a:as, b:bs) = [((as, b:bs), a), ((a:as, bs), b)]

-- DP
type Memo a b = Map.Map a b
type DP a b = a -> State (Memo a b) b

dp :: Ord a => DP a b -> DP a b
dp f x = do
  memo <- gets (Map.lookup x)
  case memo of
       Just y  -> return y
       Nothing -> do
         y <- f x
         modify (Map.insert x y)
         return y

evalDP :: DP a b -> Memo a b -> a -> b
evalDP f m x = evalState (f x) m

evalDPAll :: DP a b -> [a] -> [b]
evalDPAll f xs = evalState (sequence (map f xs)) Map.empty


-- State.hs

newtype State s x = State { runState :: s -> (x, s) }

instance Functor (State s) where
    fmap = M.liftM

instance Applicative (State s) where
    pure x = State $ \s -> (x, s)
    (<*>) = M.ap

instance Monad (State s) where
    m >>= k = State $ \s ->
        let (x, s0) = runState m s
        in runState (k x) s0

get :: (State s) s
get = State $ \s -> (s, s)

put :: s -> (State s) ()
put s = State $ \_ -> ((), s)

state :: (s -> (a, s)) -> (State s) a
state f = do
    s <- get
    let (a, s') = f s
    put s'
    return a

modify :: (s -> s) -> (State s) ()
modify f = get >>= put . f

gets :: (s -> a) -> (State s) a
gets f = get >>= return . f

evalState :: State s x -> s -> x
evalState = (fst .) . runState

execState :: State s x -> s -> s
execState = (snd .) . runState

Submission Info

Judge Result