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: Accepted)

class SegmentTree:
    def __init__(self, data):
        # 単位元
        self.ide_ele = 0
        # num: n以上の最小の2のべき乗
        self.num = 2 ** (N - 1).bit_length()
        self.seg = [self.ide_ele] * 2 * self.num
        for i in range(N):
            self.seg[i + self.num - 1] = 1 << (ord(data[i]) - 97)
        for i in range(self.num - 2, -1, -1):
            self.seg[i] = self.seg[2 * i + 1] | self.seg[2 * i + 2]

    def update(self, k, x):
        k += self.num - 1
        self.seg[k] = 1 << (ord(x) - 97)
        while k:
            k = (k - 1) // 2
            self.seg[k] = self.seg[k * 2 + 1] | self.seg[k * 2 + 2]

    def query(self, left, right):
        if right <= left:
            return self.ide_ele
        left += self.num - 1
        right += self.num - 2
        res = self.ide_ele
        while right - left > 1:
            if left & 1 == 0:
                res = res | self.seg[left]
            if right & 1 == 1:
                res = res | self.seg[right]
                right -= 1
            left = left // 2
            right = (right - 1) // 2
        if left == right:
            res = res | self.seg[left]
        else:
            res = (res | self.seg[left]) | self.seg[right]
        return res


N = int(input())
S = list(input().strip())
Q = int(input())
MAX_DIGIT = 26
st = SegmentTree(S)


for i in range(Q):
    q, a, b = map(str, input().split())
    if int(q) == 1:
        a = int(a) - 1
        st.update(a, b)
    if int(q) == 2:
        a = int(a) - 1
        b = int(b)
        res = st.query(a, b)
        print(str(bin(res)).count('1'))