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 num::Num;
use proconio::input;
use proconio::marker::Usize1;

fn main() {
    input! {
        n: usize,
        q: usize,
        c: [usize; n],
        queries: [(Usize1, Usize1); q],
    }
    let mut pi: Vec<Option<usize>> = vec![None; n+1];
    let mut ps = vec![vec![]; n];
    for i in 0..n {
        if let Some(num) = pi[c[i]] {
            ps[num].push(i);
        }
        pi[c[i]] = Some(i);
    }
    let mut qs = vec![vec![]; n];
    for i in 0..q {
        let (l, r) = queries[i];
        qs[l].push((r, i));
    }

    let mut ans = vec![0; q];
    let mut d: BIT<usize> = BIT::new(n);
    for x in (0..n).rev() {
        for &y in &ps[x] {
            d.add(y, 1);
        }
        for &query in &qs[x] {
            let r = query.0;
            let i = query.1;
            ans[i] = (r-x+1) - d.sum(r);
        }
    }

    for &a in &ans {
        println!("{}", a);
    }
}

struct BIT<T> {
    n: usize,
    d: Vec<T>,
}

impl<T> BIT<T>
where
    T: Num + Copy + Clone,
{
    fn new(n: usize) -> Self {
        BIT {
            n: n,
            d: vec![T::zero(); n + 1],
        }
    }

    fn add(&mut self, mut i: usize, x: T) {
        i += 1;
        while i <= self.n {
            self.d[i] = self.d[i] + x;
            i += (i as isize & (i as isize * -1)) as usize;
        }
    }

    fn sum(&self, mut i: usize) -> T {
        let mut x = T::zero();
        i += 1;
        while i != 0 {
            x = x + self.d[i];
            i -= (i as isize & (i as isize * -1)) as usize;
        }
        x
    }

    fn sums(&self, l: usize, r: usize) -> T {
        self.sum(r - 1) - self.sum(l - 1)
    }
}