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 <bits/stdc++.h>
using namespace std;
using ll = long long;
int c[500005];
int d[500005];
int e[500005];
int a[500005];
int bit[500005];
vector<pair<int, int>> v[500005];
int n, q;
// 1 is true
// 0 is false

int esum(int l, int r) {
  int sum = 0;
  for (int i = l; i <= r; i++) {
    sum += e[i];
  }
  return sum;
}

void update(int i, int value) {
  for (; i <= n; i += i & -i) {
    bit[i] += value;
  }
}

int sum(int i) {
  int s = 0;
  for (; i > 0; i -= i & -i) {
    s += bit[i];
  }
  return s;
}

int main() {
  cin >> n >> q;
  for (int i = 1; i <= n; i++) {
    cin >> c[i];
  }
  for (int i = 1; i <= q; i++) {
    int l, r;
    cin >> l >> r;
    v[r].push_back({i, l});
  }

  for (int i = 1; i <= n; i++) {
    if (d[c[i]] != 0) {
      update(d[c[i]], -1);
    }
    d[c[i]] = i;
    update(i, 1);
    for (auto x : v[i]) {
      a[x.first] = sum(i) - sum(x.second - 1);
    }
    // for (int r = 1; r <= n; r++) {
    //   cout << c[r] << ' ';
    // }
    // cout << endl;
    // for (int r = 1; r <= n; r++) {
    //   cout << d[r] << ' ';
    // }
    // cout << endl;
    // for (int r = 1; r <= n; r++) {
    //   cout << e[r] << ' ';
    // }
    // cout << endl << "--------------------------------" << endl;
  }
  for (int i = 1; i <= q; i++) {
    cout << a[i] << endl;
  }
}