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: Wrong Answer)

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

public class AtCoderE
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine());
        string s = Console.ReadLine();

        HashSet<int>[] counts = new HashSet<int>[26];
        for (int i = 0; i < 26; i++)
        {
            counts[i] = new HashSet<int>();
        }
        for (int i = 0; i < n; i++)
        {
            int num = StringToInt(s.Substring(i, 1));
            counts[num].Add(i);
        }

        int q = int.Parse(Console.ReadLine());
        for (int i = 0; i < q; i++)
        {
            var line = Console.ReadLine();
            var words = line.Split(' ');
            int a = int.Parse(words[0]);
            if (a == 1)
            {
                int pos = int.Parse(words[1]);
                string str = s.Substring(pos - 1, 1);
                int before = StringToInt(str);
                int after = StringToInt(words[2]);
                counts[before].Remove(pos);
                counts[after].Add(pos);
            }
            else
            {
                int b = int.Parse(words[1]);
                int c = int.Parse(words[2]);
                HashSet<int> unique = new HashSet<int>();
                for (int j = b - 1; j < c; j++)
                {
                    for (int k = 0; k < 26; k++)
                    {
                        if (counts[k].Contains(j))
                        {
                            unique.Add(k);
                        }
                    }
                }
                Console.WriteLine(unique.Count);
            }
        }
    }

    private static int StringToInt(string s)
    {
        char c = (char)s[0];
        return c - 'a';
    }
}