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)

// This code is generated by [cargo-atcoder](https://github.com/tanakh/cargo-atcoder)
// Original source code:
/*
use proconio::input;
#[allow(unused_imports)]
use proconio::marker::*;
#[allow(unused_imports)]
use std::cmp::*;
#[allow(unused_imports)]
use std::collections::*;
#[allow(unused_imports)]
use std::f64::consts::*;

#[allow(unused)]
const INF: usize = std::usize::MAX / 4;
#[allow(unused)]
const M: usize = 1000000007;

fn main() {
    input! {
        n: usize,
        s: Chars,
        q: usize,
        query: [(usize, usize, String); q],
    }
    let s = s
        .into_iter()
        .map(|c| c as usize - 'a' as usize)
        .collect::<Vec<_>>();
    let mut acc = vec![vec![0; 26]; n + 1];
    for i in 1..=n {
        for j in 0..26 {
            acc[i][j] = acc[i - 1][j];
        }
        acc[i][s[i - 1]] += 1;
    }
    // eprintln!("{:?}", acc);
    let mut plus = vec![BTreeSet::new(); 26];
    let mut minus = vec![BTreeSet::new(); 26];
    'outer: for (t, i, c) in query {
        // eprintln!("{} {} {}", t, i, c);
        if t == 1 {
            let c = c.chars().nth(0).unwrap() as usize - 'a' as usize;
            for d in 0..26 {
                if plus[d].contains(&i) {
                    plus[d].remove(&i);
                    plus[c].insert(i);
                    continue 'outer;
                }
            }
            let d = s[i - 1];
            if c != d {
                plus[c].insert(i);
                minus[d].insert(i);
            }
        } else {
            let l = i;
            let r = c.parse::<usize>().ok().unwrap();
            let mut count = 0;
            for j in 0..26 {
                let pr = plus[j].range(..=r).count();
                let mr = minus[j].range(..=r).count();
                let pl = plus[j].range(..l).count();
                let ml = minus[j].range(..l).count();
                let pj = pr - pl;
                let mj = mr - ml;
                let cj = acc[r][j] - acc[l - 1][j];
                // eprintln!("{} {} {} {}", (j + 'a' as usize) as u8 as char, pj, mj, cj);
                if cj + pj - mj > 0 {
                    count += 1;
                }
            }
            println!("{}", count);
        }
    }
}
*/

fn main() {
    let exe = "/tmp/bin73D1E01A";
    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>";