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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        char[] arr = sc.next().toCharArray();
        TreeSet<Integer>[] positions = new TreeSet[26];
        for (int i = 0; i < 26; i++) {
            positions[i] = new TreeSet<>();
        }
        for (int i = 1; i <= n; i++) {
            positions[arr[i - 1] - 'a'].add(i);
        }
        int q = sc.nextInt();
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < q; i++) {
            int type = sc.nextInt();
            if (type == 1) {
                int idx = sc.nextInt();
                int prev = arr[idx - 1] - 'a';
                positions[prev].remove(idx);
                char c = sc.next().charAt(0);
                positions[c - 'a'].add(idx);
                arr[idx - 1] = c;
            } else {
                int left = sc.nextInt();
                int right = sc.nextInt();
                int count = 0;
                for (TreeSet<Integer> set : positions) {
                    Integer x = set.ceiling(left);
                    if (x != null && x <= right) {
                        count++;
                    }
                }
                sb.append(count).append("\n");
            }
        }
		System.out.print(sb);
   }
    

}