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)

// ---------- begin fenwick tree ----------
pub struct Fenwick<T> {
    zero: T,
    a: Box<[T]>,
}

impl<T> Fenwick<T>
where
    T: Copy + std::ops::Add<Output = T>,
{
    pub fn new(size: usize, zero: T) -> Fenwick<T> {
        Fenwick {
            zero: zero,
            a: vec![zero; size + 1].into_boxed_slice(),
        }
    }
    pub fn add(&mut self, mut x: usize, v: T) {
        assert!(x > 0);
        while let Some(a) = self.a.get_mut(x) {
            *a = *a + v;
            x += x & (!x + 1);
        }
    }
    pub fn sum(&self, mut x: usize) -> T {
        assert!(x < self.a.len());
        let mut res = self.zero;
        while x > 0 {
            res = res + self.a[x];
            x -= x & (!x + 1);
        }
        res
    }
}

impl<T> Fenwick<T>
where
    T: Copy + std::ops::Add<Output = T> + PartialOrd,
{
    pub fn search(&self, s: T) -> usize {
        debug_assert!(self.sum(self.a.len() - 1) >= s);
        let mut k = 1;
        while 2 * k < self.a.len() {
            k *= 2;
        }
        let mut x = 0;
        let mut w = self.zero;
        while k > 0 {
            self.a.get(x + k).map(|a| {
                if w + *a < s {
                    w = w + *a;
                    x += k;
                }
            });
            k >>= 1;
        }
        x + 1
    }
}
// ---------- end fenwick tree ----------

use proconio::*;
use proconio::marker::*;

#[fastout]
fn run() {
    input! {
        n: usize,
        q: usize,
        c: [Usize1; n],
        ask: [(Usize1, usize); q],
    }
    let mut a = vec![vec![]; n];
    for (i, c) in c.iter().enumerate() {
        a[*c].push(i);
    }
    let mut query = vec![vec![]; n];
    for (i, (l, r)) in ask.into_iter().enumerate() {
        query[l].push((r, i));
    }
    let mut bit = Fenwick::new(n, 0i32);
    for a in a.iter_mut() {
        a.reverse();
        if let Some(k) = a.pop() {
            bit.add(k + 1, 1);
        }
    }
    let mut ans = vec![0; q];
    for (l, (query, c)) in query.into_iter().zip(c.into_iter()).enumerate() {
        for (r, k) in query.into_iter() {
            ans[k] = bit.sum(r);
        }
        bit.add(l + 1, -1);
        if let Some(k) = a[c].pop() {
            bit.add(k + 1, 1);
        }
    }
    for a in ans {
        println!("{}", a);
    }
}

fn main() {
    run();
}