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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <vector>
#include <set>
#include <iostream>

struct segment_tree {
    void build(std::string const &a) {
        t.resize(4 * a.size());
        build(0, 0, a.size(), a);
    }

    void update(size_t pos, char new_value) {
        update(0, 0, t.size() / 4, pos, new_value);
    }

    int32_t get(size_t l, size_t r) {
        return get(0, 0, t.size() / 4, l, r + 1).size();
    }

private:
    std::vector<std::set<char>> t;
    void build(size_t v, size_t l, size_t r, std::string const &a) {
        if (l + 1 == r) {
            std::set<char> m;
            m.insert(a[l]);
            t[v] = m;
        } else {
            size_t mid = (l + r) / 2;
            build(2 * v + 1, l, mid, a);
            build(2 * v + 2, mid, r, a);
            for (auto elem : t[2 * v + 1]) {
                t[v].insert(elem);
            }
            for (auto elem : t[2 * v + 2]) {
                t[v].insert(elem);
            }
        }
    }

    void update(size_t v, size_t l, size_t r, size_t pos, char new_value) {
        if (l + 1 == r) {
            std::set<char> m;
            m.insert(new_value);
            t[v] = m;
        } else {
            size_t mid = (l + r) / 2;
            if (pos < mid) {
                update(2 * v + 1, l, mid, pos, new_value);
            } else {
                update(2 * v + 2, mid, r, pos, new_value);
            }
            t[v].clear();
            for (auto elem : t[2 * v + 1]) {
                t[v].insert(elem);
            }
            for (auto elem : t[2 * v + 2]) {
                t[v].insert(elem);
            }
        }
    }

    std::set<char> get(size_t v, size_t l, size_t r, size_t req_l, size_t req_r) {
        if (req_l >= req_r) {
            return std::set<char> ();
        } else if (l == req_l && r == req_r) {
            return t[v];
        } else {
            size_t mid = (l + r) / 2;
            std::set<char> cur = get(2 * v + 1, l, mid, req_l, std::min(mid, req_r));
            for (auto elem : get(2 * v + 2, mid, r, std::max(mid, req_l), req_r)) {
                cur.insert(elem);
            }
            return cur;
        }
    }
};

int main() {
    std::ios_base::sync_with_stdio(false);
    segment_tree chr;
    size_t n;
    std::string a;
    std::cin >> n >> a;
    chr.build(a);
    size_t k;
    std::cin >> k;
    while (k-- > 0) {
        size_t type;
        std::cin >> type;
        if (type == 1) {
            size_t pos;
            char ch;
            std::cin >> pos >> ch;
            chr.update(pos - 1, ch);
        } else {
            size_t l, r;
            std::cin >> l >> r;
            std::cout << chr.get(l - 1, r - 1) << '\n';
        }
    }

    return 0;
}