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: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
using VI = vector<int>;
#define rep(i, n) for (int i = 0; i < (n); i++)

int main() {
  cin.tie(nullptr); ios_base::sync_with_stdio(false);

  int n, q; cin >> n >> q;
  VI c(n); rep(i, n) cin >> c[i];
  vector<pair<int, int>> lr(q); rep(i, q) cin >> lr[i].first >> lr[i].second;
  rep(i, q) lr[i].first--;

  const int sq = 700;
  vector<tuple<int, int, int>> lri(q);
  rep(i, q) lri[i] = make_tuple(lr[i].first / sq, lr[i].second, i);
  sort(lri.begin(), lri.end());

  VI ans(q);

  VI cnt(n+1);
  int prev = -1;
  int lx, rx;
  int sum = 0;
  VI pushed;
  for (auto [ls, r, i] : lri) {
    if (ls != prev) {
      for (auto cx : pushed) cnt[cx] = 0;
      pushed.clear();
      lx = rx = r;
      prev = ls;
    }
    int l = lr[i].first;
    assert(r == lr[i].second);
    assert(rx <= r);
    int cx;
    while (lx > l) if (cnt[cx=c[--lx]]++ == 0) sum += 1, pushed.push_back(cx);
    while (lx < l) if (--cnt[cx=c[lx++]] == 0) sum -= 1;
    // while (rx > r) if (--cnt[cx=c[--rx]] == 0) sum -= 1;
    while (rx < r) if (cnt[cx=c[rx++]]++ == 0) sum += 1, pushed.push_back(cx);
    ans[i] = sum;
  }
  rep(i, q) cout << ans[i] << "\n";
}