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 Java (OpenJDK 11.0.6) (judge verdict: Wrong Answer)

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.HashSet;
import java.util.List;
import java.util.Scanner;
import java.util.Set;
import java.util.Collections;
import java.util.ArrayList;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        SimpleStringQueries solver = new SimpleStringQueries();
        solver.solve(1, in, out);
        out.close();
    }

    static class SimpleStringQueries {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int n = in.nextInt();
            char[] s = in.next().toCharArray();
            List<Set<Integer>> list = new ArrayList<>();
            for (int i = 0; i < 26; i++) {
                list.add(new HashSet<>());
            }

            for (int i = 0; i < s.length; i++) {
                Set<Integer> set = list.get(s[i] - 'a');
                set.add(i);
            }
            int q = in.nextInt();
            for (int j = 0; j < q; j++) {
                int num = in.nextInt();
                if (num == 1) {
                    int i = in.nextInt() - 1;
                    char c = in.next().charAt(0);
                    Set<Integer> fromTarget = list.get(s[i] - 'a');
                    fromTarget.remove(i);

                    Set<Integer> toTarget = list.get(c - 'a');
                    toTarget.add(i);

                    s[i] = c;
                } else {
                    int l = in.nextInt() - 1;
                    int r = in.nextInt();
                    int result = 0;
                    for (int i = 0; i < 26; i++) {
                        Set<Integer> set = list.get(i);
                        if (set.isEmpty()) {
                            continue;
                        }
                        int lpos = Collections.binarySearch(new ArrayList<>(set), l);
                        if (lpos < 0) {
                            lpos = ~lpos;
                        }
                        int rpos = Collections.binarySearch(new ArrayList<>(set), r);
                        if (rpos < 0) {
                            rpos = ~rpos;
                        }
                        if (lpos < rpos) {
                            result++;
                        }
                    }
                    out.println(result);
                }
            }
        }

    }
}