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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<iostream>
#include<vector>
#include<map>
#include<set>
#include<string>
using namespace std;

#define SEG_NUM (1<<20)

vector<map<char, int> > seg(SEG_NUM*2);

void update(int x, char newchr, char delchr){
    x += SEG_NUM;
    seg[x][newchr]++;
    seg[x][delchr]--;
    while(true){
        x /= 2;
        if(x==0)break;
        seg[x][newchr]++;
        seg[x][delchr]--;
    }
}

int find(int x, int y){
    x += SEG_NUM;
    y += SEG_NUM;
    set<char> ans;
    while(x < y){
        if(x % 2 == 1){
            for(char i='a';i<='z';++i){
                if(seg[x][i]>0){
                    ans.insert(i);
                }
            }
            x++;
        }
        x /= 2;
        if(y % 2 == 1){
            for(char i='a';i<='z';++i){
                if(seg[y-1][i]>0){
                    ans.insert(i);
                }
            }
            y--;
        }
        y /= 2;
    }
    /**
    for(auto i=ans.begin();i!=ans.end();++i){
        cout<<*i<<endl;
    }
    **/
    return ans.size();
}

int main() {
    int N;
    cin>>N;
    string S;
    cin>>S;
    for(long i=0;i<S.size();++i){
        seg[SEG_NUM+i][S[i]]++;
    }
    for(long i=0;i<S.size();++i){
        long x = i + SEG_NUM;
        while(true){
            x /= 2;
            if(x==0)break;
            seg[x][S[i]]++;
        }
    }
    int Q;
    cin>>Q;
    int query, left, right, pos;
    char newchr;
    for(int i=0;i<Q;++i){
        cin>>query;
        if(query==1){
            cin>>pos>>newchr;
            pos--;
            update(pos, newchr, S[pos]);
            S[pos] = newchr;
        }
        else{
            cin>>left>>right;
            left--;
            right--;
            cout<<find(left, right+1)<<endl;
        }
    }
}