/in/foo.cc: In function 'int main()':
/in/foo.cc:44:14: warning: format '%d' expects argument of type 'int', but argument 2 has type 'std::priority_queue<int>::size_type' {aka 'long unsigned int'} [-Wformat=]
   44 |     printf("%d", q.size /*返回优先队列中的元素个数*/ ());
      |             ~^   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |              |                                       |
      |              int                                     std::priority_queue<int>::size_type {aka long unsigned int}
      |             %ld