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 self::segment_tree::SegmentTree;
use proconio::input;
use proconio::marker::{Chars, Usize1};

fn main() {
    input! {
        n: usize,
        cv: Chars,
        q: usize,
        qv: [(usize, Usize1, String); q],
    };

    let mut st = SegmentTree::new(n);
    for i in 0..n {
        let v = 1 << (cv[i] as usize - b'a' as usize);
        st.update(i, v);
    }

    for (qt, a1, a2) in qv {
        match qt {
            1 => {
                let i = a1;
                let c = a2.chars().nth(0).unwrap();
                let v = 1 << (c as usize - b'a' as usize);
                st.update(i, v);
            }
            2 => {
                let l = a1;
                let r = a2.parse::<usize>().unwrap();
                let c = st.query(l..r).count_ones();
                println!("{}", c);
            }
            _ => unreachable!(),
        }
    }
}

mod segment_tree {
    pub struct SegmentTree {
        // n = 1 (-> 2^0) a
        // dv[0] ... [0, 1) a
        // dv[1]
        //
        // n = 2 (-> 2^1) a, b
        // dv[0] ... [0, 2) a, b
        // dv[1] ... [0, 1) a
        // dv[2] ... [1, 2) b
        // dv[3]
        //
        // n = 4 (-> 2^2) a, b, c, d
        // dv[0] ... [0, 4) a, b, c, d
        // dv[1] ... [0, 2) a, b
        // dv[2] ... [2, 4) c, d
        // dv[3] ... [0, 1) a
        // dv[4] ... [1, 2) b
        // dv[5] ... [2, 3) c
        // dv[6] ... [3, 4) d
        // dv[7]
        dv: Vec<usize>,
    }

    impl SegmentTree {
        pub fn new(n: usize) -> Self {
            let dv = vec![0usize; n.next_power_of_two() * 2];
            Self { dv }
        }

        pub fn query(&self, range: std::ops::Range<usize>) -> usize {
            self.q(&range, 0, 0..(self.dv.len() / 2))
        }

        pub fn update(&mut self, i: usize, v: usize) {
            let mut j = i + (self.dv.len() / 2) - 1;
            self.dv[j] = v;
            while j > 0 {
                j = (j - 1) >> 1;
                let l = self.dv[j * 2 + 1];
                let r = self.dv[j * 2 + 2];
                let v = l | r;
                self.dv[j] = v;
            }
        }

        fn q(&self, rq: &std::ops::Range<usize>, i: usize, ri: std::ops::Range<usize>) -> usize {
            if rq.end <= ri.start || ri.end <= rq.start {
                0
            } else if rq.start <= ri.start && ri.end <= rq.end {
                self.dv[i]
            } else {
                let m = ri.start + (ri.end - ri.start) / 2;
                let l = self.q(&rq, i * 2 + 1, ri.start..m);
                let r = self.q(&rq, i * 2 + 2, m..ri.end);
                l | r
            }
        }
    }
}
*/

fn main() {
    let exe = "/tmp/binFDFCE04D";
    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>";