priority_queue[HTML_REMOVED],less[HTML_REMOVED]> q1; //大顶堆，存储小一半的数
priority_queue[HTML_REMOVED],greater[HTML_REMOVED]> q2;
q1.size()>q2.size()
q2.push(q1.top());
q2.size() != 0
cout<<(float)(q1.top()+q2.top())/2<<endl;
q2.pop();