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# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	public void Solve(){
		
		var sb = new StringBuilder();
		var ca = S.ToCharArray();
		var BT = new BIT[26];
		for(int i=0;i<26;i++) BT[i] = new BIT(N + 10);
		for(int i=0;i<N;i++){
			BT[S[i] - 'a'].Add(i + 1, 1);
		}
		
		for(int q=0;q<Q;q++){
			var ss = rsa();
			switch(ss[0][0]){
				case '1': {
					int pos = int.Parse(ss[1]) - 1;
					char c = ss[2][0];
					BT[ca[pos] - 'a'].Add(pos + 1, -1);
					ca[pos] = c;
					BT[ca[pos] - 'a'].Add(pos + 1, 1);
				} break;
				case '2': {
					int l = int.Parse(ss[1]) - 1;
					int r = int.Parse(ss[2]) - 1;
					
					int cnt = 0;
					for(int i=0;i<26;i++){
						int cc = BT[i].Sum(r + 1) - BT[i].Sum(l);
						if(cc == 0) cnt++;
					}
					
					sb.AppendLine((26 - cnt).ToString());
				} break;
			}
		}
		
		Console.Write(sb.ToString());
	}
	int N;
	String S;
	int Q;
	public Sol(){
		N = ri();
		S = rs();
		Q = ri();
	}

	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(char sep=' '){return Console.ReadLine().Split(sep);}
	static int[] ria(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>int.Parse(e));}
	static long[] rla(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>long.Parse(e));}
	static double[] rda(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>double.Parse(e));}
}


class BIT{
	int MM;
	int n;
	int[] bit;
	public BIT(int n_){
		n = n_;
		MM = 1 << 2;
		while(MM < n * 2) MM <<= 1;
		bit = new int[MM + 1];
	}
	//1-origin!!
	public void Add(int i, int x){
		while(i <= n){
			bit[i] += x;
			i += (i&-i);
		}
	}
	
	// i=>sum(a_1,...,a_i)
	// i=0 -> return 0;
	public int Sum(int i){
		int s = 0;
		while(i > 0){
			s += bit[i];
			i -= (i&-i);
		}
		return s;
	}
}