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)

#![allow(unused_imports)]
#![allow(non_snake_case, unused)]

use std::cmp::*;
use std::collections::*;
use std::ops::*;

macro_rules! eprint {
	($($t:tt)*) => {{
		use ::std::io::Write;
		let _ = write!(::std::io::stderr(), $($t)*);
	}};
}
macro_rules! eprintln {
	() => { eprintln!(""); };
	($($t:tt)*) => {{
		use ::std::io::Write;
		let _ = writeln!(::std::io::stderr(), $($t)*);
	}};
}
macro_rules! dbg {
	($v:expr) => {{
		let val = $v;
		eprintln!("[{}:{}] {} = {:?}", file!(), line!(), stringify!($v), val);
		val
	}}
}

macro_rules! mat {
	($($e:expr),*) => { Vec::from(vec![$($e),*]) };
	($($e:expr,)*) => { Vec::from(vec![$($e),*]) };
	($e:expr; $d:expr) => { Vec::from(vec![$e; $d]) };
	($e:expr; $d:expr $(; $ds:expr)+) => { Vec::from(vec![mat![$e $(; $ds)*]; $d]) };
}

macro_rules! ok {
	($a:ident$([$i:expr])*.$f:ident()$(@$t:ident)*) => {
		$a$([$i])*.$f($($t),*)
	};
	($a:ident$([$i:expr])*.$f:ident($e:expr$(,$es:expr)*)$(@$t:ident)*) => { {
		let t = $e;
		ok!($a$([$i])*.$f($($es),*)$(@$t)*@t)
	} };
}

pub fn readln() -> String {
	let mut line = String::new();
	::std::io::stdin().read_line(&mut line).unwrap_or_else(|e| panic!("{}", e));
	line
}

macro_rules! read {
	($($t:tt),*; $n:expr) => {{
		let stdin = ::std::io::stdin();
		let ret = ::std::io::BufRead::lines(stdin.lock()).take($n).map(|line| {
			let line = line.unwrap();
			let mut it = line.split_whitespace();
			_read!(it; $($t),*)
		}).collect::<Vec<_>>();
		ret
	}};
	($($t:tt),*) => {{
		let line = readln();
		let mut it = line.split_whitespace();
		_read!(it; $($t),*)
	}};
}

macro_rules! _read {
	($it:ident; [char]) => {
		_read!($it; String).chars().collect::<Vec<_>>()
	};
	($it:ident; [u8]) => {
		Vec::from(_read!($it; String).into_bytes())
	};
	($it:ident; usize1) => {
		$it.next().unwrap_or_else(|| panic!("input mismatch")).parse::<usize>().unwrap_or_else(|e| panic!("{}", e)) - 1
	};
	($it:ident; [usize1]) => {
		$it.map(|s| s.parse::<usize>().unwrap_or_else(|e| panic!("{}", e)) - 1).collect::<Vec<_>>()
	};
	($it:ident; [$t:ty]) => {
		$it.map(|s| s.parse::<$t>().unwrap_or_else(|e| panic!("{}", e))).collect::<Vec<_>>()
	};
	($it:ident; $t:ty) => {
		$it.next().unwrap_or_else(|| panic!("input mismatch")).parse::<$t>().unwrap_or_else(|e| panic!("{}", e))
	};
	($it:ident; $($t:tt),+) => {
		($(_read!($it; $t)),*)
	};
}

pub fn main() {
	let _ = ::std::thread::Builder::new().name("run".to_string()).stack_size(32 * 1024 * 1024).spawn(run).unwrap().join();
}

const MOD: usize = 1_000_000_007;
const INF: i64 = std::i64::MAX/2;

pub trait SetMinMax {
	fn setmin(&mut self, v: Self) -> bool;
	fn setmax(&mut self, v: Self) -> bool;
}
impl<T> SetMinMax for T where T: PartialOrd {
	fn setmin(&mut self, v: T) -> bool {
		*self > v && { *self = v; true }
	}
	fn setmax(&mut self, v: T) -> bool {
		*self < v && { *self = v; true }
	}
}

pub struct UnionFind {
	data: Vec<i32>,
}

impl UnionFind {
	pub fn new(n: usize) -> Self{
		UnionFind {
			data: vec![-1;n]
		}
	}
	pub fn root(&mut self, x: usize) -> usize{
		if self.data[x]<0 {
			x
		}
		else {
			let p = self.data[x] as usize;
			self.data[x] = self.root(p) as i32;
			self.data[x] as usize
		}
	}
	pub fn unite(&mut self, x: usize, y: usize){
		let rx = self.root(x);
		let ry = self.root(y);
		if rx!=ry {
			let (rx,ry) = if self.data[rx]>self.data[ry] {
				(rx,ry)
			}
			else{
				(ry,rx)
			};
			self.data[rx] += self.data[ry];
			self.data[ry] = rx as i32;
		}
	}
	pub fn same(&mut self, x: usize, y: usize) ->  bool{
		self.root(x) == self.root(y)
	}
	pub fn size(&mut self, x: usize) -> i32 {
		let r = self.root(x);
		- self.data[r]
	}
}

#[derive(Clone)]
struct BitSet {
    size: usize,
    a: Vec<usize>,
}

fn bit_size() -> usize {
    8 * std::mem::size_of::<usize>()
}

fn quot_rem(n: usize) -> (usize, usize) {
    let w = bit_size();
    (n / w, n % w)
}

#[allow(dead_code)]
impl BitSet {
    fn new(size: usize) -> Self {
        let w = bit_size();
        BitSet {
            size: size,
            a: vec![0; (size + w - 1) / w],
        }
    }
    fn set_at(&mut self, x: usize) {
        assert!(x < self.size);
        let (q, r) = quot_rem(x);
        self.a[q] |= 1 << r;
    }
    fn clear_at(&mut self, x: usize) {
        assert!(x < self.size);
        let (q, r) = quot_rem(x);
        self.a[q] &= !(1 << r);
    }
    fn get_at(&self, x: usize) -> bool {
        if x >= self.size {
            return false;
        }
        let (q, r) = quot_rem(x);
        (self.a[q] >> r) & 1 == 1
    }
    fn any(&self) -> bool {
        self.a.iter().any(|a| *a != 0)
    }
    fn fix(&mut self) {
        let (q, r) = quot_rem(self.size);
        if r != 0 {
            self.a[q] &= (1 << r) - 1;
        }
    }
    fn clear(&mut self) {
        let len = self.a.len();
        self.a.clear();
        self.a.resize(len, 0);
    }
    fn truncate(&mut self, len: usize) {
        if len >= self.size {
            return;
        }
        let w = bit_size();
        self.a.truncate((len + w - 1) / w);
        self.size = len;
        self.fix();
    }
    fn popcnt(&self) -> usize {
        self.a.iter().fold(0, |s, a| s + a.count_ones() as usize)
    }
    fn shift_left(&self, rhs: usize) -> Self {
        let (q, r) = quot_rem(rhs);
        let mut ans = BitSet::new(self.size + rhs);
        if r == 0 {
            for (x, y) in ans.a[q..].iter_mut().zip(self.a.iter()) {
                *x = *y;
            }
        } else {
            let w = bit_size();
            let mut prev = 0;
            for (x, y) in ans.a[q..].iter_mut().zip(self.a.iter()) {
                *x = (*y << r) | (prev >> (w - r));
                prev = *y;
            }
            *ans.a.last_mut().unwrap() |= prev >> (w - r);
        }
        ans.fix();
        ans
    }
    fn shift_right(&self, rhs: usize) -> Self {
        if rhs >= self.size {
            return BitSet::new(1);
        }
        let (q, r) = quot_rem(rhs);
        let mut ans = BitSet::new(self.size - rhs);
        if r == 0 {
            for (x, y) in ans.a.iter_mut().zip(self.a[q..].iter()) {
                *x = *y;
            }
        } else {
            let w = bit_size();
            let mut prev = 0;
            for (x, y) in ans.a.iter_mut().zip(self.a[q..].iter()).rev() {
                *x |= (*y >> r) | (prev << (w - r));
                prev = *y;
            }
        }
        ans.fix();
        ans
    }
    fn bitwise_or(&self, rhs: &Self) -> Self {
        let (x, y) = if self.size >= rhs.size {(self, rhs)} else {(rhs, self)};
        let mut a = x.a.clone();
        for (a, y) in a.iter_mut().zip(y.a.iter()) {
            *a |= *y;
        }
        BitSet {
            size: x.size,
            a: a,
        }
    }
    fn bitwise_and(&self, rhs: &Self) -> Self {
        let (x, y) = if self.size <= rhs.size {(self, rhs)} else {(rhs, self)};
        let mut a = x.a.clone();
        for (a, y) in a.iter_mut().zip(y.a.iter()) {
            *a &= *y;
        }
        BitSet {
            size: x.size,
            a: a,
        }
    }
    fn bitwise_xor(&self, rhs: &Self) -> Self {
        let (x, y) = if self.size >= rhs.size {(self, rhs)} else {(rhs, self)};
        let mut a = x.a.clone();
        for (a, y) in a.iter_mut().zip(y.a.iter()) {
            *a ^= *y;
        }
        BitSet {
            size: x.size,
            a: a,
        }
    }
    fn bitwise_or_assign(&mut self, rhs: &Self) {
        if self.size < rhs.size {
            self.size = rhs.size;
            self.a.resize(rhs.a.len(), 0);
        }
        for (a, b) in self.a.iter_mut().zip(rhs.a.iter()) {
            *a |= *b;
        }
    }
    fn bitwise_and_assign(&mut self, rhs: &Self) {
        if self.size > rhs.size {
            self.size = rhs.size;
            self.a.resize(rhs.a.len(), 0);
        }
        for (a, b) in self.a.iter_mut().zip(rhs.a.iter()) {
            *a &= *b;
        }
    }
    fn bitwise_xor_assign(&mut self, rhs: &Self) {
        if self.size < rhs.size {
            self.size = rhs.size;
            self.a.resize(rhs.a.len(), 0);
        }
        for (a, b) in self.a.iter_mut().zip(rhs.a.iter()) {
            *a ^= *b;
        }
    }
}

// 平方分割
pub struct SquareDecomp{
    v: Vec<char>,
    n: usize,
    b: usize,
    squares: Vec<BitSet>,
}

impl SquareDecomp{
    pub fn new(v: Vec<char>) -> Self {
        let n = v.len();
        let b = (n as f64).sqrt() as usize;
        SquareDecomp{
            v: v,
            n: n,
            b: b,
            squares: vec![BitSet::new(26);n/b+1]
        }
    }
    pub fn init(&mut self) {
        for i in 0..self.n/self.b+1 {
			let mut sum = 0;
			let mut seen = vec![false;26];
            for j in 0..self.b {
                let idx = i*self.b + j;
				if idx>=self.n {break;}
				let val = (self.v[idx] as usize - 'a' as usize) as usize;
				seen[val] = true;
			}
			let mut bs = BitSet::new(26);
			for j in 0..26 {
				if !seen[j] {
					bs.set_at(j);
				}
			}
			self.squares[i] = bs.clone();
			let cs = bs.clone();
			// println!("{}", cs.popcnt());
        }
	}

	pub fn update(&mut self, p: usize, c: char){
		self.v[p] = c;
		// println!("{}", c);
		let tmp = c as usize - 'a' as usize;
		let mut seen = vec![false;26];
		for i in 0..self.b {
			let idx = (p/self.b)*self.b + i;
			if idx>=self.n {break;}
			let val = (self.v[idx] as usize - 'a' as usize) as usize;
			seen[val] = true;
		}
		let mut bs = BitSet::new(26);
		for j in 0..26 {
			if !seen[j] {
				bs.set_at(j);
			}
		}
        self.squares[p/self.b] = bs;
	}

    pub fn query(&self, s: usize, t: usize) -> i64 {
        let mut idx = s;
		let mut ans = BitSet::new(26);
		for i in 0..26 {
			ans.set_at(i);
		}
        loop {
            if idx>=t {break;}
            if idx%self.b==0 && (idx+self.b-1)<t {
				ans.bitwise_and_assign(&self.squares[idx/self.b]);
				// println!("{} {}", ans.popcnt(), idx);
                idx += self.b;
                continue;
            }
            for i in 0..self.b {
				if idx>=t {break;}
				let val = (self.v[idx] as usize - 'a' as usize);
				ans.clear_at(val);
				// println!("{}", val);
                idx += 1;
                if idx%self.b==0 {break;}
            }
        }
        (26-ans.popcnt()) as i64
    }
}

fn solve() {
	let n = read!(usize);
	let s = read!(String);
	let q = read!(usize);

	let mut c = s.chars().collect::<Vec<char>>();
	let mut sq = SquareDecomp::new(c);
	sq.init();

	for i in 0..q {
		let (query,a,b) = read!(usize,usize,String);
		if query==1 {
			sq.update(a-1,b.chars().collect::<Vec<char>>()[0]);
		}
		else {
			let l = a-1;
			let r: usize = b.parse().unwrap();
			let ret = sq.query(l,r);
			println!("{}", ret);
		}
	}
	
}

fn run() {
    solve();
}