class MedianFinder {
private:
    // vector<int> counts(101, 0);
    map<int, int> counts;
    int nums = 0;

public:
    /** initialize your data structure here. */
    MedianFinder() {
    }
    
    void addNum(int num) {
        /* 计数排序 */
        counts[num]++;
        nums++;
    }
    
    double findMedian() {
        int cur = 0;

        if (nums % 2) {
                auto it = counts.begin();
                int cur = it->second;
                while (cur * 2 < nums) {
                    it++;
                    cur += it->second;
                }

                return it->first;
        }
        else {
            auto it = counts.begin();
            int cur = it->second;
            while (cur * 2 < nums) {
                it++;
                cur += it->second;
            }

            auto next = it;
            next++;
            if (cur * 2 == nums)
                return (next->first + it->first) / 2.0;
            else {   
                return it->first;
            }
        }

        return 0;
    }
};

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