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::str::FromStr;
use std::fmt::Debug;
use std::cmp;

#[derive(Debug)]
pub struct SegmentTree {
    v: Vec<Vec<i64>>,
    n: usize,
}

impl SegmentTree {
    pub fn new(a: &Vec<usize>) -> SegmentTree {
        let mut n = 1;
        while n < a.len() {
            n *= 2;
        }
        let mut v: Vec<Vec<i64>> = vec![vec![0;26]; 2 * n - 1];
        for i in 0..a.len() {
            v[n - 1 + i][a[i]] += 1;
        }

        for i in (0..n - 1).rev() {
            for j in 0..26{
                v[i][j] = v[i * 2 + 1][j] + v[i * 2 + 2][j];
            }

        }

        SegmentTree { v, n }
    }

    pub fn replace(&mut self, c: usize, pos: usize){
        //let old_c = *self.v[self.n -1 + pos].iter().filter(|x| **x == 1).nth(1).unwrap();
        let old_c: usize = self.v[self.n -1 + pos].iter()
            .enumerate()
            .filter(|(_, x)| **x == 1)
            .nth(0)
            .unwrap().0;
        self._update(0, old_c, pos, -1, 0, self.v.len()/2 + 1);
        self._update(0, c, pos, 1, 0, self.v.len()/2 + 1);

    }

    fn _update(&mut self, k: usize, c: usize, pos: usize, val: i64, l: usize, r: usize) {
        // node[k] covers [l, r)
        if pos == l && l == r - 1{
            self.v[k][c] += val;
            return;
        }

        if l <= pos && pos < r {
            self.v[k][c] += val;
            self._update(2 * k + 1, c, pos, val, l, (l + r) / 2);
            self._update(2 * k + 2, c, pos, val, (l + r) / 2, r);
        }
    }

    pub fn get_sum(&mut self, a: usize, b: usize) -> i64 {
        self._get_sum(a, b, 0, 0, (self.v.len() + 1) / 2)
            .iter()
            .filter(|x| **x > 0)
            .count() as i64
    }

    fn _get_sum(&mut self, a: usize, b: usize, k: usize, l: usize, r: usize) -> Vec<i64> {
        if b <= l || r <= a {
            return vec![0;26];
        }

        if a <= l && r <= b {
            return self.v[k].clone();
        }
        let mut res = self._get_sum(a, b, 2 * k + 1, l, (l + r) / 2);
        let tmp = self._get_sum(a, b, 2 * k + 2, (l + r) / 2, r);
        for i in 0..26{
            res[i] += tmp[i];
        }

        return res;
    }
}

#[allow(dead_code)]
fn read_as_vec<T>() -> Vec<T>
where T: FromStr, <T as FromStr>::Err : Debug{
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().split_whitespace().map(|c| T::from_str(c).unwrap()).collect()

}

#[allow(dead_code)]
fn read_as_string() -> String{
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().to_string()
}

fn main(){
    let _n = read_as_vec::<usize>()[0];
    let s = read_as_string().chars().map(|x| x as usize - 'a' as usize).collect::<Vec<usize>>();
    let q = read_as_vec::<usize>()[0];
    let mut seq = SegmentTree::new(&s);
    for _ in 0..q{
        let line = read_as_string();
        let mut it = line.split_whitespace();
        let t = it.next().unwrap().parse::<u32>().unwrap();
        if t == 1{
            let i = it.next().unwrap().parse::<usize>().unwrap()-1;
            let c = it.next().unwrap().parse::<char>().unwrap() as usize - 'a' as usize;
            seq.replace(c, i);
        }else{
            let l = it.next().unwrap().parse::<usize>().unwrap()-1;
            let r = it.next().unwrap().parse::<usize>().unwrap()-1;
            let res = seq.get_sum(l, r+1);
            println!("{}", res);
        }
    }

}

*/

fn main() {
    let exe = "./binXXXXXX";
    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>";