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)

use std::io;
use std::str::FromStr;

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

fn input_vec() -> Vec<String> {
    let mut line: String = String::new();
    io::stdin().read_line(&mut line);
    line.split_whitespace().map(|s| s.to_string()).collect()
}

fn binary_search<F>(mut ok: i32, mut ng: i32, is_ok: F) -> i32
    where
        F: Fn(usize) -> bool
    {
        while (ok - ng).abs() > 1 {
            let mid = (ok + ng) / 2;
            if is_ok(mid as usize) {
                ok = mid;
            } else {
                ng = mid;
            }
        }
        ok
}

fn main() {
    let n: u64 = input();
    let s: String = input();
    let mut s: Vec<char> = s.chars().collect();
    let q: u64 = input();
    let mut char_indices: Vec<Vec<usize>> = vec![Vec::new(); 26];
    for i in 0..s.len() {
        // println!("{}", s[i] as usize - 49);
        char_indices[s[i] as usize - 97].push(i);
    }
    // println!("{:?}", char_indices);

    for _ in 0..q {
        let query = input_vec();
        if query[0] == "1" {
            let idx: usize = query[1].parse().unwrap();
            let idx = idx - 1;
            let from_char = s[idx];
            let to_char = query[2].chars().next().unwrap();

            let target_idx = char_indices[from_char as usize - 97].binary_search(&idx).ok().unwrap();
            char_indices[from_char as usize - 97].remove(target_idx);

            s[idx] = to_char;
            let target_idx = char_indices[to_char as usize - 97].binary_search(&idx).err().unwrap();
            char_indices[to_char as usize - 97].insert(target_idx, idx);
        } else {
            let left: i32 = query[1].parse().unwrap();
            let left = left - 1;
            let right: i32 = query[2].parse().unwrap();
            let right = right - 1;
            let mut sum = 0;
            for each_indices in &char_indices {
                if each_indices.len() == 0 {
                    continue;
                }
                let left_idx = binary_search(each_indices.len() as i32, -1, |idx| {
                    each_indices[idx] as i32 >= left
                });

                let right_idx = binary_search(-1, each_indices.len() as i32, |idx| {
                    right >= each_indices[idx] as i32
                });
                // println!("{}, {}", left_idx, right_idx);
                if left_idx <= right_idx {
                    sum += 1;
                }
            }
            println!("{}", sum);
            // println!("{:?}", char_indices);
        }
    }
}