Find Median from Data Stream

class MedianFinder {
private:
    multiset<int> nums;
    multiset<int>::iterator mid;

public:
    MedianFinder() {
        mid = nums.begin();
    }

    void addNum(int num) {
        if (nums.empty()) {
            nums.insert(num);
            mid = nums.begin();
        } else if (num >= *mid && (int) nums.size() % 2 == 0) {
            nums.insert(num);
            mid++;
        } else if (num < *mid && (int) nums.size() % 2 == 1) {
            nums.insert(num);
            mid--;
        } else {
            nums.insert(num);
        }
    }

    double findMedian() {
        double ans = *mid;
        if ((int) nums.size() % 2 == 0) {
            auto it = mid; it++;
            ans += *it;
            ans /= 2.0;
        }

        return ans;
    }
};

/**
 * Your MedianFinder object will be instantiated and called as such:
 * MedianFinder* obj = new MedianFinder();
 * obj->addNum(num);
 * double param_2 = obj->findMedian();
 */