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)

#[allow(unused)]
use {
    std::error::Error,
    std::fmt::Debug,
    std::str::FromStr,
    std::io::prelude::*,
    std::io::{stdin, stdout, BufReader, BufWriter},
    std::collections::{HashSet, BinaryHeap},
    std::cmp::min,
};

type BoxResult<T> = Result<T, Box<dyn std::error::Error>>;

fn main() -> BoxResult<()> {
    let mut scanner = Scanner::new(stdin());
    
    let (n, q) = scanner.read_two::<usize, usize>()?;
    let vals = scanner.read_vector::<usize>()?;
    let mut query = vec![];
    for i in 0..q {
        let (a, b) = scanner.read_two::<usize, usize>()?;
        query.push((a - 1, b - 1, i));
    }
    
    let ans = solve(n, q, &vals, &mut query);
    let mut writer = BufWriter::new(stdout());
    for i in 0..q {
        writeln!(&mut writer, "{}", ans[i])?;
    }

    Ok(())
}

fn solve(n: usize, q: usize, vals: &[usize], query: &mut Vec<(usize, usize, usize)>) -> Vec<i64> {
    let mut ans = vec![0; q];
    query.sort_by(|a, b| a.1.cmp(&b.1));
    let mut index = 0;
    let mut right_most = vec![std::usize::MAX; n + 1];
    let mut bit = BinaryIndexedTree::new(n);
    for &(l, r, i) in query.iter() {
        while index <= r {
            if right_most[vals[index]] == std::usize::MAX {
                right_most[vals[index]] = index;
                bit.add(index, 1);
            } else {
                let prv = right_most[vals[index]];
                right_most[vals[index]] = index;
                bit.add(prv, -1);
                bit.add(index, 1);
            }
            index += 1;
        }
        let a = bit.query(l, r);
        ans[i] = a;
    }
    ans
}

pub struct BinaryIndexedTree {
    len: usize,
    values: Vec<i64>,
}

impl BinaryIndexedTree {
    pub fn new(n: usize) -> Self {
        Self {
            len: n + 1,
            values: vec![0; n + 1],
        }
    }

    pub fn add(&mut self, i: usize, x: i64) {
        let mut index = i + 1;
        while index < self.len {
            self.values[index] += x;
            let inc = index & (!index + 1);
            index += inc;
        }
    }

    pub fn query(&mut self, l: usize, r: usize) -> i64 {
        if l > 0 {
            self.get(r) - self.get(l - 1)
        } else {
            self.get(r)
        }
    }

    fn get(&mut self, i: usize) -> i64 {
        let mut index = i + 1;
        let mut sum = 0;
        while index > 0 {
            sum += self.values[index];
            let dec = index & (!index + 1);
            index -= dec;
        }
        sum
    }
}

pub struct Scanner<R> {
    reader: BufReader<R>,
    buffer: String,
}
impl<R> Scanner<R>
where
    R: Read,
{
    pub fn new(inner: R) -> Scanner<R> {
        let reader = BufReader::new(inner);
        let buffer = String::new();
        Scanner {
            reader: reader,
            buffer: buffer,
        }
    }
    pub fn with_capacity(capacity: usize, inner: R) -> Scanner<R> {
        let reader = BufReader::with_capacity(capacity, inner);
        let buffer = String::new();
        Scanner {
            reader: reader,
            buffer: buffer,
        }
    }
    pub fn read_line(&mut self) -> BoxResult<String> {
        self.reader.read_line(&mut self.buffer)?;
        let cloned = self.buffer.trim().to_string();
        self.buffer.clear();
        Ok(cloned)
    }
 
    pub fn read<T>(&mut self) -> BoxResult<T>
    where
        T: FromStr,
        T::Err: Debug + Error + 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let parsed = self.buffer.trim().parse()?;
        self.buffer.clear();
        Ok(parsed)
    }
    pub fn read_two<T, U>(&mut self) -> BoxResult<(T, U)>
    where
        T: FromStr + Copy,
        T::Err: Debug + Error + 'static,
        U: FromStr + Copy,
        U::Err: Debug + Error + 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let (a, b) = {
            let params = self.buffer.trim().split_whitespace().collect::<Vec<_>>();
            let a = params[0].parse()?;
            let b = params[1].parse()?;
            (a, b)
        };
        self.buffer.clear();
        Ok((a, b))
    }
    pub fn read_three<T, U, V>(&mut self) -> BoxResult<(T, U, V)>
    where
        T: FromStr + Copy,
        T::Err: Debug + Error + 'static,
        U: FromStr + Copy,
        U::Err: Debug + Error + 'static,
        V: FromStr + Copy,
        V::Err: Debug + Error + 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let (a, b, c) = {
            let params = self.buffer.trim().split_whitespace().collect::<Vec<_>>();
            let a = params[0].parse()?;
            let b = params[1].parse()?;
            let c = params[2].parse()?;
            (a, b, c)
        };
        self.buffer.clear();
        Ok((a, b, c))
    }
    pub fn read_four<T, U, V, W>(&mut self) -> BoxResult<(T, U, V, W)>
    where
        T: FromStr + Copy,
        T::Err: Debug + Error + 'static,
        U: FromStr + Copy,
        U::Err: Debug + Error + 'static,
        V: FromStr + Copy,
        V::Err: Debug + Error + 'static,
        W: FromStr + Copy,
        W::Err: Debug + Error + 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let (a, b, c, d) = {
            let params = self.buffer.trim().split_whitespace().collect::<Vec<_>>();
            let a = params[0].parse()?;
            let b = params[1].parse()?;
            let c = params[2].parse()?;
            let d = params[3].parse()?;
            (a, b, c, d)
        };
        self.buffer.clear();
        Ok((a, b, c, d))
    }
    pub fn read_vector<T>(&mut self) -> BoxResult<Vec<T>>
    where
        T: FromStr + Copy,
        T::Err: Debug + Error + 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let parsed_vec = self
            .buffer
            .trim()
            .split_whitespace()
            .map(|s| s.parse())
            .collect::<Result<Vec<_>, _>>()?;
        self.buffer.clear();
        Ok(parsed_vec)
    }
    pub fn read_matrix<T>(&mut self, lines: u64) -> BoxResult<Vec<Vec<T>>>
    where
        T: FromStr + Copy,
        T::Err: Debug + Error + 'static,
    {
        let mut parsed_matrix = vec![];
        for _ in 0..lines {
            self.reader.read_line(&mut self.buffer)?;
            parsed_matrix.push(
                self.buffer
                    .trim()
                    .split_whitespace()
                    .map(|s| s.parse())
                    .collect::<Result<Vec<_>, _>>()?,
            );
            self.buffer.clear();
        }
        Ok(parsed_matrix)
    }
    pub fn read_chars(&mut self) -> BoxResult<Vec<char>> {
        self.reader.read_line(&mut self.buffer)?;
        let chars = self.buffer.trim().chars().collect::<Vec<_>>();
        self.buffer.clear();
        Ok(chars)
    }
}