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 std::collections::BTreeSet;
use std::ops::Bound::*;
use proconio::input;
use proconio::marker::Chars;

type RawQuery = (usize, usize, String);

fn main() {
    input! {
        n: usize,
        mut s: Chars,
        q: usize,
        queries: [(usize, usize, String); q],
    }

    let mut v_set = vec![BTreeSet::new(); 26];
    for (i, &c) in s.iter().enumerate() {
        let ind = alph_to_int(c);
        v_set[ind].insert(i);
    }

    for query in queries {
        let query = parse_query(query);

        match query {
            Query::Change(i, c) => {
                let i = i - 1;
                let prev_c = s[i];
                let prev_c_int = alph_to_int(prev_c);
                v_set[prev_c_int].remove(&(i));

                let c_int = alph_to_int(c);
                v_set[c_int].insert(i);

                s[i] = c;
            },
            Query::Count(l, r) => {
                let l = l - 1;
                let r = r - 1;
                let mut count = 0;
                for i in 0..26 {
                    let set = &v_set[i];
                    let mut range = set.range((Included(l), Included(r)));
                    let contains = range.next().is_some();

                    if contains {
                        count += 1;
                    }
                }

                println!("{}", count);
            }
        }

        // eprintln!("{:?}", query);
        // eprintln!("{:?}", v_set);
    }
}

#[derive(Debug)]
enum Query {
    Change(usize, char),
    Count(usize, usize),
}

fn parse_query(query: RawQuery) -> Query {
    let qtype = query.0;

    if qtype == 1 {
        let c = query.2.chars().next().unwrap();
        Query::Change(query.1, c)
    } else {
        let r: usize = query.2.parse().unwrap();
        Query::Count(query.1, r)
    }
}

fn alph_to_int(c: char) -> usize {
    c as usize - 'a' as usize
}

#[cfg(test)]
mod tests {
    use super::*;

#[test]
    fn alph_to_int_test() {
        assert_eq!(0, alph_to_int('a'));
        assert_eq!(25, alph_to_int('z'));
    }
}
*/

fn main() {
    let exe = "/tmp/bin1EE4825C";
    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>";