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 (Clang 3.8.0) (judge verdict: Accepted)

#include <iostream>
#include <algorithm>
#include <iomanip>
#include <string>
#include <vector>
#include <math.h>
#include <queue>
#include <deque>
#include <map>
#include <set>
const int MOD = 1e9+7;
typedef long long ll;
using namespace std;

int ctoi(char c){
	return (int)(c - 'a');
}

int main(){
	int n, q;
	string s;
	cin >> n >> s >> q;
	vector<set<int> > st(26);
	for (int i = 0; i < s.length(); i++){
		st[ctoi(s[i])].insert(i);
	}
	for (int i = 0; i < q; i++){
		int x;
		cin >> x;
		if (x == 1){
			int a;
			char c;
			cin >> a >> c;
			st[ctoi(s[a-1])].erase(a-1);
			st[ctoi(c)].insert(a-1);
			s[a-1] = c;
		}else{
			int a, b;
			cin >> a >> b;
			int coun = 0;
			for (int j = 0; j < 26; j++){
				auto iter1 = st[j].lower_bound(a-1);
				if (*iter1 <= b-1 && iter1 != st[j].end()) coun++;
			}
			cout << coun << endl;
		}
	}
	return 0;
}