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:
/*
#[allow(unused_macros)]
macro_rules! debug {
	($($a:expr),*) => {
		println!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
	}
}

pub struct SegmentTree<T, F> {
	seg: Vec<T>,
	n: usize,
	f: F,
	initial_value: T,
}

impl<T: Copy, F> SegmentTree<T, F>
where
	F: Fn(T, T) -> T,
{
	pub fn new(size: usize, initial_value: T, f: F) -> SegmentTree<T, F> {
		let mut m = 1;
		while m <= size {
			m <<= 1;
		}
		SegmentTree {
			seg: vec![initial_value; m * 2],
			n: m,
			f: f,
			initial_value: initial_value,
		}
	}

	pub fn update(&mut self, k: usize, value: T) {
		let mut k = k;
		k += self.n - 1;
		self.seg[k] = value;
		while k > 0 {
			k = (k - 1) >> 1;
			self.seg[k] = (self.f)(self.seg[k * 2 + 1], self.seg[k * 2 + 2]);
		}
	}

	/// Get the minimum value in the array in the range [a, b)
	///
	/// # Panics
	///
	/// Panics if `a >= b`.
	pub fn query(&self, a: usize, b: usize) -> T {
		assert!(a < b);
		self.query_range(a, b, 0, 0, self.n)
	}

	fn query_range(&self, a: usize, b: usize, k: usize, l: usize, r: usize) -> T {
		if r <= a || b <= l {
			self.initial_value
		} else if a <= l && r <= b {
			self.seg[k]
		} else {
			let x = self.query_range(a, b, k * 2 + 1, l, (l + r) >> 1);
			let y = self.query_range(a, b, k * 2 + 2, (l + r) >> 1, r);
			(self.f)(x, y)
		}
	}
}

use std::cmp::{max, min};
#[allow(dead_code)]
const MOD: usize = 1e9 as usize + 7;

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

	let n: usize = sc.read();
	let s: Vec<usize> = sc
		.read::<String>()
		.chars()
		.map(|c| c as usize - 'a' as usize)
		.collect();
	let mut seg = SegmentTree::new(n, 0, |a, b| a | b);
	for i in 0..n {
		seg.update(i, 1 << s[i]);
	}

	let q: usize = sc.read();
	for _ in 0..q {
		let t: usize = sc.read();
		if t == 1 {
			let pos: usize = sc.read::<usize>() - 1;
			let c = sc.read_chars()[0] as usize - 'a' as usize;
			seg.update(pos, 1 << c)
		} else {
			let l = sc.read::<usize>() - 1;
			let r = sc.read::<usize>();
			let ans: usize = seg.query(l, r);
			println!("{}", ans.count_ones());
		}
	}
}

pub struct IO<R, W: std::io::Write>(R, std::io::BufWriter<W>);

impl<R: std::io::Read, W: std::io::Write> IO<R, W> {
	pub fn new(r: R, w: W) -> IO<R, W> {
		IO(r, std::io::BufWriter::new(w))
	}
	pub fn write<S: std::ops::Deref<Target = str>>(&mut self, s: S) {
		use std::io::Write;
		self.1.write(s.as_bytes()).unwrap();
	}
	pub fn read<T: std::str::FromStr>(&mut self) -> T {
		use std::io::Read;
		let buf = self
			.0
			.by_ref()
			.bytes()
			.map(|b| b.unwrap())
			.skip_while(|&b| b == b' ' || b == b'\n' || b == b'\r' || b == b'\t')
			.take_while(|&b| b != b' ' && b != b'\n' && b != b'\r' && b != b'\t')
			.collect::<Vec<_>>();
		unsafe { std::str::from_utf8_unchecked(&buf) }
			.parse()
			.ok()
			.expect("Parse error.")
	}
	pub fn read_vec<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
		(0..n).map(|_| self.read()).collect()
	}
	pub fn read_chars(&mut self) -> Vec<char> {
		self.read::<String>().chars().collect()
	}
	pub fn read_char_grid(&mut self, n: usize) -> Vec<Vec<char>> {
		(0..n).map(|_| self.read_chars()).collect()
	}
	pub fn read_pairs<T: std::str::FromStr, U: std::str::FromStr>(
		&mut self,
		n: usize,
	) -> Vec<(T, U)> {
		(0..n)
			.map(|_| (self.read::<T>(), self.read::<U>()))
			.collect::<Vec<(T, U)>>()
	}
	pub fn read_matrix<T: std::str::FromStr>(&mut self, n: usize, m: usize) -> Vec<Vec<T>> {
		(0..n)
			.map(|_| (0..m).map(|_| self.read()).collect())
			.collect()
	}
}
*/

fn main() {
    let exe = "/tmp/binFE314B2D";
    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>";