Confusion

As you know our star "gachn" is a rising star in competitive programming but nowadays he is upset because of a task was given to him by his mentor. His teacher gave him a task: The task is that he has been given an array of N integers. his teacher gave him Q queries to solve. For each query he has to tell the teacher the number of distinct integers from Ai.Ai+1.Ai+2.......AN.

Example:

Input:  n = 5, q = 3, a = {1, 2, 3, 2, 1}, queries = {2, 1, 4}

Output:

3
3
2

Approach:

C++

#include <bits/stdc++.h>
using namespace std;

int main()
{
    int n = 5, q = 3;

    vector<int> a = {1, 2, 3, 2, 1};
    vector<int> queries = {2, 1, 4};
    int distinct[n];
    int dNums = 0;
    set<int> numbers;

    for (int i = n - 1; i >= 0; i--)
    {
        if (numbers.count(a[i]) == 0)
        {
            numbers.insert(a[i]);
            distinct[i] = ++dNums;
        }
        else
            distinct[i] = dNums;
    }
    for (int i = 0; i < q; i++)
    {

        cout << distinct[queries[i] - 1] << endl;
    }

    return 0;
}