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)

struct FenwickTree {
    n: usize,
    v: Vec<i32>,
}

impl FenwickTree {
    fn new(n: usize) -> FenwickTree {
        FenwickTree {
            n,
            v: vec![0; n + 1],
        }
    }

    fn add(&mut self, mut i: usize, x: i32) {
        while i <= self.n {
            self.v[i] += x;
            i += i & (!i + 1);
        }
    }

    fn sum(&self, mut i: usize) -> i32 {
        let mut res = 0;
        while i > 0 {
            res += self.v[i];
            i -= i & (!i + 1);
        }
        res
    }
}

use std::io::{BufRead, Write};
use std::collections::VecDeque;

fn main () {
    let stdin = std::io::stdin();
    let stdout = std::io::stdout();
    let mut reader = std::io::BufReader::new(stdin.lock());
    let mut writer = std::io::BufWriter::new(stdout.lock());

    let (n, q): (usize, usize) = {
        let mut buf = String::new();
        reader.read_line(&mut buf).unwrap();
        let mut iter = buf.split_whitespace();
        (
            iter.next().unwrap().parse().unwrap(),
            iter.next().unwrap().parse().unwrap(),
        )
    };
    
    let c: Vec<usize> = {
        let mut buf = String::new();
        reader.read_line(&mut buf).unwrap();
        let iter = buf.split_whitespace();
        iter.map(|x| x.parse::<usize>().unwrap() - 1).collect()
    };

    let mut ft = FenwickTree::new(n);
    let mut v = vec![VecDeque::new(); n];
    for i in (0..n).rev() {
        if v[c[i]].is_empty() {
            ft.add(i + 1, 1);
        }
        v[c[i]].push_front(i);
    }

    let mut l: Vec<usize> = Vec::with_capacity(q);
    let mut r: Vec<usize> = Vec::with_capacity(q);
    for _ in 0..q {
        let mut buf = String::new();
        reader.read_line(&mut buf).unwrap();
        let mut iter = buf.split_whitespace();
        l.push(iter.next().unwrap().parse::<usize>().unwrap() - 1);
        r.push(iter.next().unwrap().parse().unwrap());
    }

    let mut order: Vec<usize> = (0..q).collect();
    order.sort_by(|&i, &j| r[j].cmp(&r[i]));

    let mut ans = vec![0; q];
    let mut i = n;
    for j in order {
        while r[j] < i {
            i -= 1;
            v[c[i]].pop_back();
            ft.add(i + 1, -1);
            if let Some(k) = v[c[i]].back() {
                ft.add(k + 1, 1);
            }
        }
        ans[j] = ft.sum(n) - ft.sum(l[j]);
    }

    for i in 0..q {
        writeln!(writer, "{}", ans[i]).unwrap();
    }
}