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)]
use std::cmp::*;
use std::collections::*;
use std::io::Write;

#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

fn main() {
    let n = read::<usize>();
    let mut s = read::<String>()
        .chars()
        .map(|x| x.to_digit(36).unwrap() as usize - 10)
        .collect::<Vec<_>>();
    let q = read::<usize>();
    let mut queries = vec![];
    for i in 0..q {
        let v = read_vec::<String>();
        queries.push(v);
    }
    let mut counts = vec![SegTree::new(n, 0i64); 26];
    for i in 0..n {
        counts[s[i]].update(i, 1);
    }

    for query in queries {
        if query[0] == "1" {
            let i = usize::from_str_radix(&query[1], 10).unwrap() - 1;
            let c = usize::from_str_radix(&query[2], 36).unwrap() - 10;
            let cur = counts[s[i]].query(i, i + 1);
            counts[s[i]].update(i, cur - 1);
            let cur = counts[c].query(i, i + 1);
            counts[c].update(i, cur + 1);
            s[i] = c;
        } else {
            let l = usize::from_str_radix(&query[1], 10).unwrap() - 1;
            let r = usize::from_str_radix(&query[2], 10).unwrap() - 1;
            let mut ans = 0;
            for ref count in counts.iter() {
                if count.query(l, r + 1) >= 1 {
                    ans += 1;
                }
            }
            println!("{}", ans);
        }
    }
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

#[derive(Debug, Clone)]
struct SegTree {
    n: usize,
    dat: Vec<i64>,
    init: i64,
}

impl SegTree {
    fn new(n: usize, init: i64) -> SegTree {
        let mut m = 1;
        // For simplicity, we use 2 ** n sized SegTree.
        while m < n {
            m *= 2;
        }
        SegTree {
            n: m,
            dat: vec![init; 2 * m - 1],
            init: init,
        }
    }

    // dat[k] = a;
    fn update(&mut self, k: usize, a: i64) {
        let mut k = k;
        k += self.n - 1;
        self.dat[k] = a;
        while k > 0 {
            k = (k - 1) / 2;
            self.dat[k] = self.dat[k * 2 + 1] + self.dat[k * 2 + 2];
        }
    }

    // [a, b)
    fn query(&self, a: usize, b: usize) -> i64 {
        self.query_inner(a, b, 0, 0, self.n)
    }

    fn query_inner(&self, a: usize, b: usize, k: usize, l: usize, r: usize) -> i64 {
        if r <= a || b <= l {
            return self.init;
        }
        if a <= l && r <= b {
            return self.dat[k];
        }

        let vl = self.query_inner(a, b, k * 2 + 1, l, (l + r) / 2);
        let vr = self.query_inner(a, b, k * 2 + 2, (l + r) / 2, r);
        vl + vr
    }
}