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: Time Limit Exceeded)

// This code is generated by [cargo-atcoder](https://github.com/tanakh/cargo-atcoder)
// Original source code:
/*
mod utils;
use std::io::Write;
use std::collections::BTreeSet;

fn main() {
    let mut scanner = utils::StdinScanner::new();
    let mut writer = utils::StdoutWriter::new();

    let n: usize = scanner.read();
    let mut s = scanner.readl().to_owned();
    let q: usize = scanner.read();

    dbg!(n, &s, q);

    let mut v = vec![BTreeSet::<usize>::new(); 28];

    for (i, b) in s.bytes().enumerate() {
        let idx = (b - b'a') as usize;
        v[idx].insert(i);
    }

    for _ in 0..q {
        let o: u8 = scanner.read();
        let l = scanner.read::<usize>() - 1;
        let r = scanner.reads();

        if o == 1 {
            let r = r.as_bytes()[0];
            if s.as_bytes()[l] != r {
                let old_idx = s.as_bytes()[l] - b'a';
                let new_idx = r - b'a';

                unsafe {
                    s.as_bytes_mut()[l] = r;
                }

                v[old_idx as usize].remove(&l);
                v[new_idx as usize].insert(l);
            }
        } else if o == 2 {
            let r = r.parse::<usize>().unwrap() - 1;
            let total = v.iter().filter(|t| t.range(l..=r).count() > 0).count();
            writeln!(writer, "{}", total).unwrap();
        }
    }
}
*/

fn main() {
    let exe = "/tmp/bin74D11256";
    std::io::Write::write_all(&mut std::fs::File::create(exe).unwrap(), &decode(BIN)).unwrap();
    std::fs::set_permissions(exe, std::os::unix::fs::PermissionsExt::from_mode(0o755)).unwrap();
    std::process::exit(std::process::Command::new(exe).status().unwrap().code().unwrap())
}

fn decode(v: &str) -> Vec<u8> {
    let mut ret = vec![];
    let mut buf = 0;
    let mut tbl = vec![64; 256];
    for i in 0..64 { tbl[TBL[i] as usize] = i as u8; }
    for (i, c) in v.bytes().filter_map(|c| { let c = tbl[c as usize]; if c < 64 { Some(c) } else { None } }).enumerate() {
        match i % 4 {
            0 => buf = c << 2,
            1 => { ret.push(buf | c >> 4); buf = c << 4; }
            2 => { ret.push(buf | c >> 2); buf = c << 6; }
            3 => ret.push(buf | c),
            _ => unreachable!(),
        }
    }
    ret
}

const TBL: &'static [u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
const BIN: &'static str = "<base64-encoded ELF executable removed>";