Problem:
Score : 900 points

Problem Statement

There are N Snukes lining up in a row.
You are given a string S of length N. The i-th Snuke from the front has two red balls if the i-th character in S is 0; one red ball and one blue ball if the i-th character in S is 1; two blue balls if the i-th character in S is 2.

Takahashi has a sequence that is initially empty. Find the number of the possible sequences he may have after repeating the following procedure 2N times, modulo 998244353:

Each Snuke who has one or more balls simultaneously chooses one of his balls and hand it to the Snuke in front of him, or hand it to Takahashi if he is the first Snuke in the row.

Takahashi receives the ball and put it to the end of his sequence.

Constraints

1 \leq |S| \leq 2000

S consists of 0,1 and 2.

Note that the integer N is not directly given in input; it is given indirectly as the length of the string S.

Input

Input is given from Standard Input in the following format:

S

Output

Print the number of the possible sequences Takahashi may have after repeating the procedure 2N times, modulo 998244353.

Sample Input 1

02

Sample Output 1

3

There are three sequences that Takahashi may have: rrbb, rbrb and rbbr, where r and b stand for red and blue balls, respectively.

Sample Input 2

1210

Sample Output 2

55

Sample Input 3

12001021211100201020

Sample Output 3

543589959

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

{-# LANGUAGE
  ScopedTypeVariables, BangPatterns, TupleSections, ExplicitForAll,
  LambdaCase, MultiWayIf, Unsafe, RecordWildCards, FlexibleContexts, CPP,
  NoMonomorphismRestriction, GADTs,
  RankNTypes, EmptyDataDecls, EmptyCase, ViewPatterns #-}

import Data.Bits
import Data.List
import qualified Data.ByteString.Char8 as BS
import qualified Data.ByteString.Lazy.Char8 as BSL
import Data.IntMap.Strict (IntMap)
import qualified Data.IntMap.Strict as IMS
import qualified Data.IntMap.Lazy as IML
import Data.IntSet (IntSet)
import qualified Data.IntSet as IS
import qualified Data.Sequence as Seq
import Data.Sequence (Seq)
import qualified Data.Array.IArray as A
import qualified Data.Array.MArray.Safe as A
import qualified Data.Array.MArray as A
import Data.Array (Array)
import Data.Array.Unboxed (UArray)
import Data.Array.IArray (IArray)
import Data.Array.MArray.Safe (MArray)
import Data.Array.IO.Safe (IOArray, IOUArray)
import Data.Array.ST.Safe (STArray, STUArray, runSTArray, runSTUArray)
import qualified Data.Vector as V
import qualified Data.Vector.Unboxed as VU
import qualified Data.Vector.Unboxed.Mutable as VUM
import Control.Monad
import Control.Monad.ST
-- import Control.Monad.ST.Safe
import Control.Applicative
import Data.Maybe
import Data.Tuple
import Data.Ord
import Control.Monad.State.Strict
import Data.Int
import Data.Word
import System.IO
import Data.Function
import Control.Monad.Primitive
import qualified Data.Vector.Primitive.Mutable as VPM
import qualified Data.Vector.Generic.Mutable as VGM
import Data.STRef
import Data.IORef

main :: IO ()
main = do
  input <- BS.getLine
  let n = BS.length input
      blues = VU.map (subtract (fromEnum '0') . fromEnum)
              $ VU.unfoldrN n BS.uncons input
      (!vec_aftern,!bleft_aftern,!b,!r) = VU.ifoldl'
        (\(!vec_prev,!bleft_prev,!b_prev,!r_prev) !i !b_this ->
           let !len_prev = VU.length vec_prev
               !b = b_prev + b_this
               !r = r_prev + 2 - b_this
               !bleft = bleft_prev + sl
               !vec = VU.zipWith plus (VU.cons 0 vec_prev) (VU.snoc vec_prev 0)
               sl | r <= i - bleft_prev            = 1 | otherwise = 0
               sr | b <= bleft_prev + len_prev - 1 = 1 | otherwise = 0
           in (VU.slice sl (len_prev + 1 - sl - sr) vec,bleft,b,r))
        (VU.singleton 1, 0, 0, 0) blues
      (!vec_last,!bleft_last) = foldl'
        (\(!vec_prev,!bleft_prev) !i ->
           let !len_prev = VU.length vec_prev
               !vec = VU.zipWith plus (VU.cons 0 vec_prev) (VU.snoc vec_prev 0)
               !bleft = bleft_prev + sl
               sl | r <= i-1 - bleft_prev          = 1 | otherwise = 0
               sr | b <= bleft_prev + len_prev - 1 = 1 | otherwise = 0
           in (VU.slice sl (len_prev + 1 - sl - sr) vec, bleft))
        (vec_aftern,bleft_aftern) [n+1..2*n]
  print $ vec_last VU.! 0
        

{-# INLINE plus #-}
plus :: Int -> Int -> Int
plus = \x y -> let xpy = x+y in if xpy >= modulus then xpy - modulus else xpy


{-# INLINE modulus #-}
modulus :: (Integral i) => i
modulus = 998244353

{-# INLINE nprime #-}
nprime :: Word64
nprime = 998244351

{-# INLINE rsq #-}
rsq :: Word64
rsq = 932051910

newtype Montgomery = Mon {unMon :: Word32}
  deriving (Eq, Show)

instance Num Montgomery where
  {-# INLINE (+) #-}
  (+) = monAdd
  {-# INLINE (*) #-}
  (*) = monMult
  {-# INLINE (-) #-}
  (-) = monSub
  {-# INLINE negate #-}
  negate (Mon x) = Mon (modulus - x)
  {-# INLINE fromInteger #-}
  fromInteger = monRep . fromInteger
  {-# INLINE signum #-}
  signum x | x == Mon 0 = Mon 0
           | otherwise  = monRep 1
  {-# INLINE abs #-}
  abs = id

{-# INLINE monMult #-}
monMult :: Montgomery -> Montgomery -> Montgomery
monMult (Mon x) (Mon y) = Mon $ monRed $ fromIntegral x * fromIntegral y

{-# INLINE monAdd #-}
monAdd :: Montgomery -> Montgomery -> Montgomery
monAdd (Mon x) (Mon y) = Mon $ x+y + if x >= modulus-y then modulus else 0
    
{-# INLINE monSub #-}
monSub :: Montgomery -> Montgomery -> Montgomery
monSub (Mon x) (Mon y) = Mon $ x-y + if x < y then modulus else 0

{-# INLINE monRep #-}
monRep :: Word32 -> Montgomery
monRep x = Mon $ monRed $ rsq * fromIntegral x

{-# INLINE fromMon #-}
fromMon :: Montgomery -> Word32
fromMon (Mon x) = monRed $ fromIntegral x

{-# INLINE monRed #-}
monRed :: Word64 -> Word32
monRed x = t - if t >= modulus then modulus else 0
  where t = fromIntegral $ (`shiftR` 32) $ x + x*nprime .&.mask32 *modulus

mask32 :: Word64
mask32 = bit 32 - 1

rInt :: StateT BSL.ByteString Maybe Int
rInt = StateT $ BSL.readInt . BSL.dropWhile (<'!')

#define D(f,r,d) f::Integral a=>a->d;f=fromIntegral;r::String->d;r=read
#define C(f,r,g,h,d) D(f,r,d);g,h::RealFrac a=>a->d;g=floor;h=ceiling
C(_toInteger_,readInteger,floorInteger,ceilInteger,Integer)
C(toInt,readInt,floorInt,ceilInt,Int)
C(toI8,readI8,floorI8,ceilI8,Int8)
C(toI16,readI16,floorI16,ceilI16,Int16)
C(toI32,readI32,floorI32,ceilI32,Int32)
C(toI64,readI64,floorI64,ceilI64,Int64)
C(toWord,readWord,floorWord,ceilWord,Word)
C(toW8,readW8,floorW8,ceilW8,Word8)
C(toW16,readW16,floorW16,ceilW16,Word16)
C(toW32,readW32,floorW32,ceilW32,Word32)
C(toW64,readW64,floorW64,ceilW64,Word64)
D(toDouble,readDouble,Double)
D(toFloat,readFloat,Float)
#undef D
#undef C


#define N(f,g,a,m)\
  f :: forall e i s. (C(a,m)A.Ix i) => (i,i) -> e -> m (a i e); f=A.newArray;\
  g :: forall e i s. (C(a,m)A.Ix i) => (i,i) -> m (a i e); g=A.newArray_
#define C(a,m)
N(newIOA,newIOA_,IOArray,IO)
N(newSTA,newSTA_,STArray s,ST s)
#undef C
#define C(a,m) MArray (a) e (m), 
N(newIOUA,newIOUA_,IOUArray,IO)
N(newSTUA,newSTUA_,STUArray s,ST s)
#undef C
#undef N