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;
use proconio::marker::{Chars, Usize1};

pub trait Monoid {
  fn empty() -> Self;
  fn append(&self, other: &Self) -> Self;
}

pub struct SegmentTree<T>
where
  T: Monoid + Clone + Copy,
{
  size: usize,
  data: Vec<T>,
}

impl<T> SegmentTree<T>
where
  T: Monoid + Clone + Copy,
{
  pub fn new(size: usize) -> Self {
    let mut n = 1;
    while n < size {
      n *= 2;
    }
    let size = n;
    let data = vec![T::empty(); size * 2 - 1];
    Self { size, data }
  }

  pub fn from_slice(values: &[T]) -> Self {
    let mut st = SegmentTree::new(values.len());
    for (i, v) in values.into_iter().enumerate() {
      st.data[i + st.size - 1] = *v;
    }
    if st.size < 2 {
      return st;
    }
    for i in (0..=(st.size - 2)).rev() {
      st.data[i] = st.data[i * 2 + 1].append(&st.data[i * 2 + 2]);
    }
    st
  }

  // 0-origin
  pub fn update(&mut self, i: usize, v: T) {
    let mut i = i + self.size - 1;
    self.data[i] = v;
    while i > 0 {
      i = (i - 1) / 2;
      self.data[i] = self.data[i * 2 + 1].append(&self.data[i * 2 + 2]);
    }
  }

  // [a, b)
  // 0-origin
  pub fn query(&self, a: usize, b: usize) -> T {
    self.execute_query(a, b, 0, 0, self.size)
  }

  fn execute_query(&self, a: usize, b: usize, i: usize, l: usize, r: usize) -> T {
    if r <= a || b <= l {
      return T::empty();
    }
    if a <= l && r <= b {
      return self.data[i];
    }
    let vl = self.execute_query(a, b, i * 2 + 1, l, (l + r) / 2);
    let vr = self.execute_query(a, b, i * 2 + 2, (l + r) / 2, r);
    vl.append(&vr)
  }
}

impl Monoid for u32 {
  fn empty() -> Self {
    0
  }
  fn append(&self, other: &Self) -> Self {
    *self | *other
  }
}

fn main() {
  input! {
    _n: usize,
    s: Chars,
  };

  let st_value = s
    .into_iter()
    .map(|ch| {
      let n: u32 = ch.into();
      let m = n - 97;
      1 << m
    })
    .collect::<Vec<_>>();
  let mut st = SegmentTree::from_slice(&st_value);

  input! { q: usize };
  for _ in 0..q {
    input! { k: usize }
    match k {
      1 => {
        input! { a: Usize1, b: char };
        let b: u32 = b.into();
        let n = b - 97;
        st.update(a, 1 << n);
      }
      2 => {
        input! { a: Usize1, b: usize };
        let x = st.query(a, b);
        let mut res = 0;
        for i in 0..26 {
          if (x >> i) & 1 == 1 {
            res += 1;
          }
        }
        println!("{}", res);
      }
      _ => {}
    }
  }
}
*/

fn main() {
    let exe = "/tmp/binAE46D1F7";
    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>";