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 (3.4.3) (judge verdict: Time Limit Exceeded)

import bisect
import collections

def main():
    n = int(input())

    s = input()

    q = int(input())

    li = [x for x in s]

    d = {}
    d = collections.defaultdict(lambda:[])

    for x in [chr(i) for i in range(97, 97 + 26)]:
        d[x] = []

    for i, x in enumerate(s):
        d[x].append(i)


    for _ in range(q):
        a, *x = input().split()

        if a == "1":
            i = int(x[0]) - 1
            c = x[1]
            index = bisect.bisect_left(d[li[i]], i)
            d[li[i]].pop(index)
            d[c].insert(bisect.bisect_left(d[c], i), i)
            li[i] = c
        else:
            l = int(x[0]) - 1
            r = int(x[1]) - 1
            cnt = 0
            for v in d.values():
                index = bisect.bisect_left(v, l)
                if index == len(v):
                    continue
                if v[index] <= r:
                    cnt += 1
            print(cnt)

main()