Problem:
Score : 600 points

Problem Statement

We have N colored balls arranged in a row from left to right; the color of the i-th ball from the left is c_i.

You are given Q queries. The i-th query is as follows: how many different colors do the l_i-th through r_i-th balls from the left have?

Constraints

1\leq N,Q \leq 5 \times 10^5

1\leq c_i \leq N

1\leq l_i \leq r_i \leq N

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N Q
c_1 c_2 \cdots c_N
l_1 r_1
l_2 r_2
:
l_Q r_Q

Output

Print Q lines. The i-th line should contain the response to the i-th query.

Sample Input 1

4 3
1 2 1 3
1 3
2 4
3 3

Sample Output 1

2
3
1

The 1-st, 2-nd, and 3-rd balls from the left have the colors 1, 2, and 1 - two different colors.

The 2-st, 3-rd, and 4-th balls from the left have the colors 2, 1, and 3 - three different colors.

The 3-rd ball from the left has the color 1 - just one color.

Sample Input 2

10 10
2 5 6 5 2 1 7 9 7 2
5 5
2 4
6 7
2 2
7 8
7 9
1 8
6 9
8 10
6 8

Sample Output 2

1
2
2
1
2
2
6
3
3
3

Solution in Rust (1.42.0) (judge verdict: Accepted)

use proconio::{input, marker::Usize1};

fn main() {
    input!(n: usize, q: usize, c: [Usize1; n], lr: [(Usize1, usize); q]);
    let mut queries: Vec<_> = lr
        .into_iter()
        .enumerate()
        .map(|(i, (l, r))| (l, r, i))
        .collect();
    let k = (n as f64).sqrt() as usize;
    queries.sort_by_key(|&(l, r, _)| (l / k, if l / k % 2 == 0 { r } else { n - r }));
    let mut mul = vec![0; n];
    let mut kind = 0;
    #[inline]
    fn add(i: usize, c: &[usize], kind: &mut usize, mul: &mut [usize]) {
        if mul[c[i]] == 0 {
            *kind += 1;
        }
        mul[c[i]] += 1;
    }
    #[inline]
    fn sub(i: usize, c: &[usize], kind: &mut usize, mul: &mut [usize]) {
        mul[c[i]] -= 1;
        if mul[c[i]] == 0 {
            *kind -= 1;
        }
    }
    let mut i = 0;
    let mut j = 0;
    let mut ans = vec![None; q];
    for (l, r, query_id) in queries {
        while j < r {
            add(j, &c, &mut kind, &mut mul);
            j += 1;
        }
        while l < i {
            i -= 1;
            add(i, &c, &mut kind, &mut mul);
        }
        while r < j {
            j -= 1;
            sub(j, &c, &mut kind, &mut mul);
        }
        while i < l {
            sub(i, &c, &mut kind, &mut mul);
            i += 1;
        }
        ans[query_id] = Some(kind);
    }
    for x in ans.iter().copied().map(Option::unwrap) {
        println!("{}", x);
    }
}