[Microsoft] How to find if a number is present equal to or more than n/2 times in an array of size n?

find_number.cc

/* Error!!
void helper(const vector<int> &vec, int pos, pair<int, int> &curr) {
    for (int i = pos; i < vec.size(); ++i) {
        if (curr.second == 0 || curr.first == vec[i] ) {
            curr = make_pair(vec[i], curr.second + 1);
        } else {
            --curr.second;
        }
    }
}

int find_number(const vector<int> &vec) {
    if (vec.empty()) {
        return -1; // Error
    }
    pair<int, int> curr(vec[0], 1);
    helper(vec, 2, curr); //ignore vec[1]
    if (curr.second <= 0) {
        curr = make_pair(vec[1], 1);
        helper(vec, 2, curr); //ignore vec[0]
        if (curr.second <= 0) {
            curr = make_pair(vec[0], 1); //here vec[0] must equal to vec[1]
        }
    }
    return curr.first;
}
*/