int binarySearch(vector<int> arrayToSearch, int key, int L, int R) {
    int size = (int)arrayToSearch.size();
    int half = size / 2 - 1;
    if(key == arrayToSearch[half]) {
        return half;
    } else if(key > arrayToSearch[half]) {
        binarySearch(arrayToSearch, key, half+1, R);
    } else {
        binarySearch(arrayToSearch, key, L, half - 1);
    }
    return -1;
}