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 C++ (GCC 9.2.1) (judge verdict: Accepted)

#include <cstdio>
#include <algorithm>
#include <vector>
#include <utility>

using i8 = std::int8_t;
using u8 = std::uint8_t;
using i16 = std::int16_t;
using u16 = std::uint16_t;
using i32 = std::int32_t;
using u32 = std::uint32_t;
using i64 = std::int64_t;
using u64 = std::uint64_t;
using i128 = __int128_t;
using u128 = __uint128_t;
using usize = std::size_t;

template<typename T, size_t MAX_N>
class BIT
{
	public:
		BIT(size_t n) : _bit(), _n(n) {}

		T sum(size_t i)
		{
			T r = 0;
			while (i > 0)
			{
				r += _bit[i];
				i &= (i - 1);
			}
			return r;
		}

		void add(size_t i, T x)
		{
			while (i <= _n)
			{
				_bit[i] += x;
				i += i & -i;
			}
		}

	protected:
		T _bit[MAX_N + 1];
		size_t _n;
};

i32 a[500001];
i32 ans[500000];
i32 last_appear[500001];

using range = std::pair<i32, i32>;
using query = std::pair<i32, range>;

std::vector<query> vq;

auto main() -> i32 {
	i32 n, q;
	scanf("%d%d", &n, &q);
	BIT<i32, 500004> bit(n);
	for (i32 i = 0; i < n; ++i) {
		scanf("%d", a + i + 1);
	}
	for (i32 i = 0; i < q; ++i) {
		i32 l, r;
		scanf("%d%d", &l, &r);
		vq.emplace_back(i, range(l, r));
	}
	std::sort(vq.begin(), vq.end(), [](const auto& a, const auto& b) { return a.second.second < b.second.second; });

	i32 rindex = 1;
	for (auto& q : vq) {
		auto [l, r] = q.second;
		while (rindex <= r) {
			if (last_appear[a[rindex]] != 0) {
				bit.add(last_appear[a[rindex]], -1);
			}
			last_appear[a[rindex]] = rindex;
			bit.add(rindex, 1);
			rindex += 1;
		}
		i32 res = bit.sum(r) - bit.sum(l - 1);
		ans[q.first] = res;
	}

	for (i32 i = 0; i < q; ++i) {
		printf("%d\n", ans[i]);
	}

	return 0;
}