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::*;

struct SegmentTree {
    n: usize,
    x: Vec<u32>,
}
impl SegmentTree {
    fn new(n: usize) -> Self {
        Self {
            n: n,
            x: vec![0; n * 2],
        }
    }
    fn update(&mut self, i: usize, x: u32) {
        let mut i = self.n + i - 1;
        self.x[i] = x;
        while i > 0 {
            i = (i - 1) / 2;
            self.x[i] = self.x[i * 2 + 1] | self.x[i * 2 + 2];
        }
    }
    fn rng(&self, r: std::ops::Range<usize>) -> u32 {
        self.rng_impl(0, r, 0..self.n)
    }
    fn rng_impl(&self, k: usize, r: std::ops::Range<usize>, a: std::ops::Range<usize>) -> u32 {
        if r.end <= a.start || a.end <= r.start {
            0
        } else if r.start <= a.start && a.end <= r.end {
            self.x[k]
        } else {
            self.rng_impl(k * 2 + 1, r.clone(), a.start..(a.start + a.end) / 2)
                | self.rng_impl(k * 2 + 2, r, (a.start + a.end) / 2..a.end)
        }
    }
}

fn cnv(c: u8) -> u32 {
    1 << (c - ascii::AsciiChar::a as u8)
}

fn main() {
    input! {
        n:usize,
        s:Bytes,
        q:usize,
    }

    let mut st = SegmentTree::new(1 << 19);
    for i in 0..n {
        st.update(i, cnv(s[i]))
    }

    for _ in 0..q {
        input! { t : u8 }
        if t == 1 {
            input! { i : Usize1, c : char }
            st.update(i, cnv(c as u8))
        } else {
            input! { l : Usize1, r : usize }
            println!("{}", st.rng(l..r).count_ones())
        }
    }
}
*/

fn main() {
    let exe = "/tmp/binD4F269A3";
    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>";