查找数据里的中位数

使用两个堆，算法思路如下图所示。

class MedianFinder {
public:
    /** initialize your data structure here. */
    priority_queue<double> maxPQ;
    priority_queue<double, vector<double>, greater<double> > minPQ;
    MedianFinder() {

    }
    
    void addNum(int num) {
        if (maxPQ.empty()) {
            maxPQ.push(num);
            return;
        }
        if (maxPQ.size() == minPQ.size()) {
            if (num < maxPQ.top())
                maxPQ.push(num);
            else
                minPQ.push(num);
        }
        else if (maxPQ.size() == minPQ.size() + 1) {
            if (num < maxPQ.top()) {
                minPQ.push(maxPQ.top());
                maxPQ.pop();
                maxPQ.push(num);
            }
            else
                minPQ.push(num);
        }
        else if (maxPQ.size() + 1 == minPQ.size()) {
            if (num < minPQ.top())
                maxPQ.push(num);
            else {
                maxPQ.push(minPQ.top());
                minPQ.pop();
                minPQ.push(num);
            }
        }
    }
    
    double findMedian() {
        if (maxPQ.size() == minPQ.size())
            return (maxPQ.top() + minPQ.top()) / 2;
        else if (maxPQ.size() > minPQ.size())
            return maxPQ.top();
        else
            return minPQ.top();
    }
};

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