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# (.NET Core 3.1.201) (judge verdict: Accepted)

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

class MainClass
{
    static void Main()
    {
        int N = int.Parse(Console.ReadLine());
        var S = new List<char>() { '?' };
        S.AddRange(Console.ReadLine().ToList());
        int Q = int.Parse(Console.ReadLine());

        var bit = new BIT[26];
        for(int i = 0; i < 26; i++)
        {
            bit[i] = new BIT(N+1);
        }
        for (int i = 1; i < N+1; i++)
        {
            char s = S[i];
            bit[s - 'a'].add(i, 1);
        }

        var ans = new List<int>();
        for (int i = 0; i < Q; i++)
        {
            var Query = Console.ReadLine().Split();
            if (Query[0] == "1")
            {
                int a = int.Parse(Query[1]);
                char b = Query[2][0];
                int num = bit[S[a] - 'a'].sum(a+1) - bit[S[a] - 'a'].sum(a);

                bit[S[a] - 'a'].add(a, -num);
                bit[b-'a'].add(a, num);
                S[a] = b;
            }
            else if(Query[0]=="2")
            {
                int a = int.Parse(Query[1]), b = int.Parse(Query[2]);
                int num = 0;
                for(int j = 0; j < 26; j++)
                {
                    if (bit[j].sum(b+1) - bit[j].sum(a) > 0) num++;
                }
                ans.Add(num);
            }
        }
        foreach(int i in ans)
            Console.WriteLine(i);
    }
}
//初期は0の集合
class BIT
{
    private int[] bit;
    private int N;
    public BIT(int n)
    {
        bit = new int[n + 1];
        N = n;
    }

    public int sum(int i)
    {
        int s = 0;
        while (i > 0)
        {
            s += bit[i];
            i -= (i & -i);
        }
        return s;
    }

    public void add(int i, int x)
    {
        i++;
        while (i <= N)
        {
            bit[i] += x;
            i += (i & (-i));
        }
    }
}