Problem:
Score : 500 points

Problem Statement

You are given a string S of length N consisting of lowercase English letters.

Process Q queries of the following two types:

Type 1: change the i_q-th character of S to c_q. (Do nothing if the i_q-th character is already c_q.)

Type 2: answer the number of different characters occurring in the substring of S between the l_q-th and r_q-th characters (inclusive).

Constraints

N, Q, i_q, l_q, and r_q are integers.

S is a string consisting of lowercase English letters.

c_q is a lowercase English letter.

1 \leq N \leq 500000

1 \leq Q \leq 20000

|S| = N

1 \leq i_q \leq N

1 \leq l_q \leq r_q \leq N

There is at least one query of type 2 in each testcase.

Input

Input is given from Standard Input in the following format:

N
S
Q
Query_1
\vdots
Query_Q

Here, Query_i in the 4-th through (Q+3)-th lines is one of the following:

1 i_q c_q

2 l_q r_q

Output

For each query of type 2, print a line containing the answer.

Sample Input 1

7
abcdbbd
6
2 3 6
1 5 z
2 1 1
1 4 a
1 7 d
2 1 7

Sample Output 1

3
1
5

In the first query, cdbb contains three kinds of letters: b , c , and d, so we print 3.

In the second query, S is modified to abcdzbd.

In the third query, a contains one kind of letter: a, so we print 1.

In the fourth query, S is modified to abcazbd.

In the fifth query, S does not change and is still abcazbd.

In the sixth query, abcazbd contains five kinds of letters: a, b, c, d, and z, so we print 5.

Solution in Haskell (GHC 7.10.3) (judge verdict: Wrong Answer)

{-# LANGUAGE OverloadedStrings #-}
import qualified Data.ByteString as BR
import qualified Data.ByteString.Char8 as B
import qualified Data.IntSet as IS
import qualified Data.ByteString.Internal as B
import Control.Monad
import Foreign.ForeignPtr
import Foreign.Storable
import qualified Data.IntMap.Strict as IM
import Data.IORef 

type Counter = IS.IntSet

data Builder = Builder !Int !Counter !(IM.IntMap Counter)

splitR :: Int -> IM.IntMap a -> (IM.IntMap a, IM.IntMap a)
splitR i m = let (l, p, r) = IM.splitLookup i m in (l, maybe id (IM.insert i) p r)

main = do
    _ <- B.getLine
    str <- B.getLine
    numQueries <- readLn
    let build (Builder i s m) c
            | IS.member c s = Builder (i + 1) s m
            | otherwise = let s' = IS.insert c s
                in Builder (i + 1) mempty (IM.insert i s' m)
    let Builder _ _ map0 = BR.foldl' (\b -> build b . fromEnum) (Builder 1 mempty mempty) str
    ref <- newIORef map0
    replicateM_ numQueries $ do
        [typ, p, q] <- B.words <$> B.getLine 
        case typ of
            "1" -> do
                base <- readIORef ref

                let i = read $ B.unpack p
                let v = BR.head q
                
                case IM.lookupGE i base of
                    Nothing -> pure ()
                    Just (k, s) -> writeIORef ref $! IM.insert k (IS.insert (fromEnum v) s) base
            "2" -> do
                base <- readIORef ref
                let i = read $ B.unpack p
                let j = read $ B.unpack q

                let (_, wing) = splitR i base
                let (body, _) = splitR (j + 1) wing
                print $ IS.size $ IS.unions $ IM.elems body