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: Accepted)

import java.io.InputStream;
import java.io.PrintStream;
import java.util.Scanner;
import java.util.SortedSet;
import java.util.TreeSet;

public class Main {

  public static void main(String[] args) {
    resolve(System.in, System.out);
  }

  static void resolve(InputStream is, PrintStream pw) {
    Scanner sc = new Scanner(is);
    int n = Integer.parseInt(sc.next());
    String s = sc.next();
    char[] sArray = s.toCharArray();
    int q = Integer.parseInt(sc.next());
    CharIndexes indexesForAllAlphabet[] = new CharIndexes[27];
    for (int i = 0; i < 27; i++) {
      indexesForAllAlphabet[i] = new CharIndexes();
    }
    for (int i = 0; i < n; i++) {
      char c = sArray[i];
      int index = c - 'a';
      indexesForAllAlphabet[index].addIndex(i);
    }
    for (int query = 0; query < q; query++) {
      int type = Integer.parseInt(sc.next());
      if (type == 1) {
        int i = Integer.parseInt(sc.next()) - 1;
        char c = sc.next().charAt(0);
        indexesForAllAlphabet[sArray[i] - 'a'].removeIndex(i);
        sArray[i] = c;
        indexesForAllAlphabet[sArray[i] - 'a'].addIndex(i);
      } else {
        int l = Integer.parseInt(sc.next()) - 1;
        int r = Integer.parseInt(sc.next()) - 1;
        int ans = 0;
        for (CharIndexes indexes : indexesForAllAlphabet) {
          if (indexes.containsIndexRange(l, r)) {
            ans++;
          }
        }
        pw.println(ans);
      }
    }
  }

  static class CharIndexes {

    SortedSet<Integer> indexes = new TreeSet<>();

    void addIndex(int index) {
      indexes.add(index);
    }

    void removeIndex(int index) {
      indexes.remove(index);
    }

    boolean containsIndexRange(int from, int endInclusive) {
      return !indexes.subSet(from, endInclusive + 1).isEmpty();
    }
  }
}