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: Time Limit Exceeded)

use std::io::*;
use std::str::FromStr;
use std::collections::HashSet;

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char) 
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

fn main() {
    let n: usize = read();
    let s: String = read();
    let q: usize = read();

    let mut chars: Vec<char> = s.chars().collect();
    let query_vec: Vec<Vec<String>> = (0..q).map(|_| (0..3).map(|_| read()).collect()).collect();

    for query in query_vec.into_iter() {
        let t: usize = query[0].parse().unwrap();
        if t == 1 {
            let i: usize = query[1].parse().unwrap();
            let c: char = query[2].chars().nth(0).unwrap();
            chars[i-1] = c;
        } else {
            let l: usize = query[1].parse().unwrap();
            let r: usize = query[2].parse().unwrap();
            let uniq: HashSet<char> = chars.clone().into_iter().skip(l-1).take(r-l+1).collect();
            println!("{}", uniq.len());
            // let v: Vec<char> = chars.clone().into_iter().skip(l-1).take(r-l+1).collect();
            // println!("{:?} {}", v, uniq.len());
        }

    }
}