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 Rust (1.15.1) (judge verdict: Accepted)

use std::io::*;
mod fenwick_tree {
    use std::ops::*;
    pub struct FenwickTree<T> {
        size: usize,
        data: Vec<T>,
        identity: T,
    }
    impl<T: Copy + Clone + AddAssign + Sub<Output = T>> FenwickTree<T> {
        pub fn new(size: usize, id: T) -> FenwickTree<T> {
            FenwickTree {
                size: size,
                data: vec![id; size + 2],
                identity: id,
            }
        }
        fn prefix_sum(&self, i: usize) -> T {
            let mut res = self.identity;
            let mut idx = i;
            while idx > 0 {
                res += self.data[idx];
                idx -= ((idx as isize) & -(idx as isize)) as usize;
            }
            res
        }
        pub fn update(&mut self, i: usize, x: T) {
            let mut idx = i;
            while idx <= self.size {
                self.data[idx] += x;
                idx += ((idx as isize) & -(idx as isize)) as usize;
            }
        }
        pub fn query(&self, l: usize, r: usize) -> T {
            self.prefix_sum(r) - self.prefix_sum(l - 1)
        }
    }
}

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let n: usize = itr.next().unwrap().parse().unwrap();
    let mut s: Vec<usize> = itr
        .next()
        .unwrap()
        .chars()
        .map(|c| c as usize - 'a' as usize)
        .collect();
    let q: usize = itr.next().unwrap().parse().unwrap();
    let mut count: Vec<fenwick_tree::FenwickTree<i64>> = (0..26)
        .map(|_| fenwick_tree::FenwickTree::new(n + 1, 0))
        .collect();
    for i in 0..s.len() {
        count[s[i]].update(i + 1, 1);
    }

    let mut out = Vec::new();
    for _ in 0..q {
        let c: usize = itr.next().unwrap().parse().unwrap();
        if c == 1 {
            let i: usize = itr.next().unwrap().parse().unwrap();
            let tmp: Vec<char> = itr.next().unwrap().chars().collect();
            let c: usize = tmp[0] as usize - 'a' as usize;
            count[s[i - 1]].update(i, -1);
            count[c].update(i, 1);
            s[i - 1] = c;
        } else {
            let l: usize = itr.next().unwrap().parse().unwrap();
            let r: usize = itr.next().unwrap().parse().unwrap();

            let mut ans = 0i64;
            for i in 0..26 {
                if count[i].query(l, r) > 0 {
                    ans += 1;
                }
            }
            writeln!(out, "{}", ans).ok();
        }
    }
    stdout().write_all(&out).unwrap();
}