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 PyPy2 (5.6.0) (judge verdict: Accepted)

# -*- coding: utf-8 -*-
import sys

N=input()
S=["None"]+list(raw_input())
Q=input()
query=[ sys.stdin.readline().split() for _ in range(Q) ]

#BIT
bit=[ [ 0 for _ in range(N+1) ] for _ in range(27) ]  #1-indexed bit[1]:aのbit, bit[2]:bのbit ...

def add(idx,a,w):
    while a<=N:
        bit[idx][a]+=w
        a+=a&-a

def sum(idx,a):
    ret=0
    while 0<a:
        ret+=bit[idx][a]
        a-=a&-a
    return ret

for i,x in enumerate(S):
    if i==0: continue
    add(ord(x)-96,i,1)  #a~zのどのbit配列か,特定文字のbit配列の何番目,bitに代入する値


for q1,q2,q3 in query:
    q1=int(q1)
    q2=int(q2)
    if q1==1:
        before_q3=S[q2] #文字列Sの変更前の文字をbefore_q3に代入
        S[q2]=q3        #文字列Sの変更部分1文字を更新
        q3=ord(q3)-96                   #変更後の文字をアスキーコード10進数で表現
        before_q3=ord(before_q3)-96     #変更前の文字をアスキーコード10進数で表現
        add(q3,q2,1)                    #a~zのどのbit配列か,特定文字のbit配列の何番目,bitに代入する値
        add(before_q3,q2,-1)    #置き代えた文字は-1しなきゃいけない
    elif q1==2:
        q3=int(q3)
        cnt=0
        for i in range(1,27):
            if 0<sum(i,q3)-sum(i,q2-1):
                cnt+=1
        print cnt