Намиране на елемент

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    int n, q, a;
    cin >> n;
    vector<int> arr(n);
    for(int i = 0; i < n; i++)
        cin >> arr[i];

    cin >> q;
    for(int i = 0; i < q; i++){
        cin >> a;
        if(arr.empty()){
            cout << 0 << endl;
            continue;
        }

        int lower = lower_bound(arr.begin(), arr.end(), a) - arr.begin();

        if(lower >= arr.size() || arr[lower] != a){
            cout << lower << endl;
            continue;
        }
        int upper = upper_bound(arr.begin(), arr.end(), a) - arr.begin() - 1;
        cout << lower << " " << upper << endl;
    }
    return 0;
}