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 PyPy3 (7.3.0) (judge verdict: Accepted)

class SegTree:
    X_unit = set()
    X_f = lambda x,y,z:y|z

    def __init__(self, N):
        self.N = N
        self.X = [self.X_unit] * (N + N)

    def build(self, seq):
        for i, x in enumerate(seq, self.N):
            self.X[i] = x
        for i in range(self.N - 1, 0, -1):
            self.X[i] = self.X_f(self.X[i << 1], self.X[i << 1 | 1])

    def set_val(self, i, x):
        i += self.N
        self.X[i] = x
        while i > 1:
            i >>= 1
            self.X[i] = self.X_f(self.X[i << 1], self.X[i << 1 | 1])

    def fold(self, L, R):
        L += self.N
        R += self.N
        vL = self.X_unit
        vR = self.X_unit
        while L < R:
            if L & 1:
                vL = self.X_f(vL, self.X[L])
                L += 1
            if R & 1:
                R -= 1
                vR = self.X_f(self.X[R], vR)
            L >>= 1
            R >>= 1
        return self.X_f(vL, vR)

N = int(input())
S = list(input())
S = [set(i) for i in S]
Q = int(input())
Tree = SegTree(N)
Tree.build(S)

for i in range(Q):
    a,b,c = input().split()
    if a == '1':
        i = int(b)-1
        c = set(c)
        Tree.set_val(i,c)
    else:
        l = int(b)-1
        r = int(c)
        print(len(Tree.fold(l,r)))