LeetCode之Find Median from Data Stream

class MedianFinder {
private:
    priority_queue<int, vector<int>,greater<int>>Greater;//小数字一半，顶部为其中最大的
    priority_queue<int, vector<int>, less<int>>Less;//大数字一半，顶部为其中最小的
    int length;
public:
    MedianFinder(){
        length = 0;
    }
    // Adds a number into the data structure.
    void addNum(int num) {
        if(length == 0){
            Greater.push(num);
            length++;
            return;
        }
        if(length % 2 == 0){//如果大堆和小堆一样大,保证小数字堆大小始终小于等于大数字堆大小（方便输出中位数Greater.top()）
            if(num >= Less.top()){//比小数字堆最大数大，插入大数字堆
                Greater.push(num);
            }
            else{//否则调整
                Greater.push(Less.top());
                Less.pop();
                Less.push(num);
            }
        }
        
        else{
             if(Less.size() == 0){//小数字堆为空
                if(num >= Greater.top()){//把输入数字给大数字堆，大数字堆原来数据给小数字堆
                    Less.push(Greater.top());
                    Greater.pop();
                    Greater.push(num);
                }
                else{//直接插小数字堆
                    Less.push(num);
                }
                length++;
                return;
             }
            if(num >= Greater.top()){//大数堆比小数堆多一个，而且比大数堆最小数大，把大堆最小插入小堆，再把num插入大堆
                Less.push(Greater.top());
                Greater.pop();
                Greater.push(num);
            }
            else{//直接插小堆
                Less.push(num);
            }
        }
        length++;
    }

    // Returns the median of current data stream
    double findMedian() {
        if(length % 2 == 0){
            float mid = (Greater.top() + Less.top())/2.0;
            return mid;
        }
        else{
            return Greater.top();//大堆中最小的为中位数
        }
    }
};