Efficient implementation Binary Search

I have an algorithmic test about implementing of binary search that works in a maximum amount of time of 2 seconds.

First, I've implemented a recursive version of binary search, but it was taking almost 3.6 seconds to finish in some test cases. Then, I changed it to an iterative version, but it takes 2.6 seconds in the same test case. However, I think that using a while loop is a reason why it takes a lot of time.

My question is: What do I need to improve to make it take a maximum 2 seconds?

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int iterBinarySearch(vector<int> A, int low, int high, int key) {
    int mid;
    while (low <= high) {
        mid = low + ((high - low)/2);
        if (key < A[mid]) {
            high = mid -1;
        } else if (key > A[mid]) {
            low = mid +1;
        } else {
            return mid;
        }
    }
    return -1;
}

int main() {

    vector<int>dict;
    vector<int>keys;

    int dictSize;
    cin >> dictSize;
    while (dictSize--) {
        int val;
        cin >> val;
        dict.push_back(val);
    }

    int keysSize;
    cin >> keysSize;
    while (keysSize--) {
        int val;
        cin >> val;
        keys.push_back(val);
    }

    sort(dict.begin(), dict.end());
    int size = (int)dict.size() -1;
    for(int i = 0; i< keys.size(); ++i) {
        if ((dict[0] > keys[i]) || (dict[size] < keys[i])) {
            cout << "-1" << ' ';
        } else {
            int res = iterBinarySearch(dict, 0, size, keys[i]);
            cout << res << ' ';
        }
    }
    return 0;
}