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 Python (3.8.2) (judge verdict: Accepted)

import sys
# import re
import math
import collections
# import decimal
import bisect
import itertools
import fractions
# import functools
import copy
# import heapq
import decimal
# import statistics
import queue

# import numpy as np

sys.setrecursionlimit(10000001)
INF = 10 ** 16
MOD = 10 ** 9 + 7
# MOD = 998244353

ni = lambda: int(sys.stdin.readline())
ns = lambda: map(int, sys.stdin.readline().split())
na = lambda: list(map(int, sys.stdin.readline().split()))


# ===CODE===
def main():
    n = ni()
    s = list(input())
    q = ni()

    alphabet_idx = {}
    for i in range(26):
        alphabet_idx[i] = []

    for i, si in enumerate(s):
        alphabet_idx[ord(si) - ord("a")].append(i)

    for _ in range(q):
        qi, a, b = input().split()
        qi, a = int(qi), int(a)

        if qi == 1:
            a -= 1
            if s[a] == b:
                continue
            del_char = ord(s[a]) - ord("a")
            del_idx = bisect.bisect_left(alphabet_idx[del_char], a)
            del alphabet_idx[del_char][del_idx]

            insert_char = ord(b) - ord("a")
            insert_idx = bisect.bisect_left(alphabet_idx[insert_char], a)
            alphabet_idx[insert_char].insert(insert_idx, a)

            s[a] = b

        if qi == 2:
            b = int(b)
            a -= 1
            b -= 1
            ans = 0

            for i in range(26):
                a_idx = bisect.bisect_left(alphabet_idx[i], a)
                if a_idx < len(alphabet_idx[i]):
                    if alphabet_idx[i][a_idx] <= b:
                        ans += 1

            print(ans)


if __name__ == '__main__':
    main()