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 (1.42.0) (judge verdict: Accepted)

#![allow(unused, non_snake_case, dead_code, non_upper_case_globals)]
use std::cmp::*;
use std::collections::*;
use std::mem::*;

fn main() {
    let (r, w, e) = (std::io::stdin(), std::io::stdout(), std::io::stderr());
    let mut io = IO::new(r.lock(), w.lock(), e.lock());

    let n = io.read::<usize>();
    let mut s = io.chars();
    let mut fws = vec![Fenwick::new(MX); 26];
    let mut tb = vec![0; MX];
    let base = 3;
    for i in 0..n {
        let fwi = i + base;
        let cind = (s[i] as u8 - b'a') as usize;
        fws[cind].update(base + i + 1, 1);
        tb[base + i + 1] = cind;
    }
    let q = io.read::<usize>();
    for _ in 0..q {
        let t = io.read::<usize>();
        match t {
            1 => {
                let iq = io.read::<usize>();
                let cq = io.chars()[0];
                let cind = (cq as u8 - b'a') as usize;
                if tb[base + iq] == cind {
                    continue;
                }
                fws[tb[base + iq]].update(base + iq, -1);
                fws[cind].update(base + iq, 1);
                tb[base + iq] = cind;
            }
            _ => {
                let lq = io.read::<usize>();
                let rq = io.read::<usize>();
                let mut sts = BTreeSet::new();
                for i in 0..26 {
                    if fws[i].query(base + rq) - fws[i].query(base + lq - 1) > 0 {
                        sts.insert(i);
                    }
                }
                io.writeln(sts.len());
            }
        }
    }
}

#[derive(Clone)]
struct Fenwick {
    n: usize,
    bit: Vec<i64>,
}
impl Fenwick {
    fn new(n: usize) -> Fenwick {
        Fenwick {
            n: n,
            bit: vec![0i64; n + 1],
        }
    }
    fn update(&mut self, a: usize, w: i64) {
        let mut x = a as isize;
        while x as usize <= self.n {
            self.bit[x as usize] += w; //-> SUM
                                       //   self.bit[x as usize] = max(self.bit[x as usize], w);
            x += 1 << x.trailing_zeros();
        }
    }
    fn query(&mut self, a: usize) -> i64 {
        let mut ret = 0;
        let mut x = a as isize;
        while x > 0 {
            ret += self.bit[x as usize]; // -> SUM QUERY
                                         //   ret = max(self.bit[x as usize], ret);
            x -= 1 << x.trailing_zeros();
        }
        ret
    }
}
static MX: usize = 1010101;
static MOD: i64 = 1000000007;
static INF: i64 = std::i64::MAX >> 1;
// IO
use std::io::*;
struct IO<R: Read, W: Write, E: Write> {
    Read: R,
    Write: BufWriter<W>,
    Error: BufWriter<E>,
}
impl<R: Read, W: Write, E: Write> IO<R, W, E> {
    fn new(r: R, w: W, e: E) -> IO<R, W, E> {
        IO {
            Read: r,
            Write: BufWriter::new(w),
            Error: BufWriter::new(e),
        }
    }
    fn read<T>(&mut self) -> T
    where
        T: std::str::FromStr,
    {
        let next: String = self
            .Read
            .by_ref()
            .bytes()
            .map(|c| c.unwrap() as char)
            .skip_while(|c| c.is_whitespace())
            .take_while(|c| !c.is_whitespace())
            .collect();
        next.parse().ok().unwrap()
    }
    fn chars(&mut self) -> Vec<char> {
        self.read::<String>().chars().collect()
    }
    fn chari(&mut self) -> Vec<i64> {
        self.chars()
            .iter()
            .map(|&c| (c as u8 - b'0') as i64)
            .collect::<Vec<i64>>()
    }
    fn readn<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read::<T>()).collect::<Vec<_>>()
    }
    fn readmat<T: std::str::FromStr>(&mut self, n: usize, m: usize) -> Vec<Vec<T>> {
        (0..n).map(|_| self.readn(m)).collect()
    }
    fn write<S: ToString>(&mut self, val: S) {
        self.Write.write(val.to_string().as_bytes());
    }
    fn writeln<S: ToString>(&mut self, val: S) {
        self.Write.write(val.to_string().as_bytes());
        self.Write.write(b"\n");
    }
    fn debug<S: std::fmt::Debug>(&mut self, val: S) {
        writeln!(self.Error, "(debug) {:?}", &val);
    }
    fn debug2<S: std::fmt::Debug, T: std::fmt::Debug>(&mut self, val1: S, val2: T) {
        writeln!(self.Error, "(debug2) {:?} -> {:?}", val1, val2);
    }
    fn debug3<S: std::fmt::Debug, T: std::fmt::Debug, U: std::fmt::Debug>(
        &mut self,
        val1: S,
        val2: T,
        val3: U,
    ) {
        writeln!(
            self.Error,
            "(debug3) {:?} -> {:?} -> {:?}",
            val1, val2, val3
        );
    }
}