堆排序：大顶堆，小顶堆

大顶堆
priority_queue<int> q;
for( int i= 0; i< 10; ++i ) q.push(i);
while( !q.empty() ){
cout<<q.top()<<endl;
q.pop();
}

小顶堆
priority_queue<int, vector<int>, greater<int> > q;
for( int i= 0; i< 10; ++i ) q.push(10-i);
while( !q.empty() ){
cout << q.top() << endl;
q.pop();
}