foo.cc: In instantiation of ‘bool Graph<T>::spfa_head(int) [with T = int]’:
foo.cc:65:20:   required from here
   65 |         bool f=g.spfa_head(1);
      |                ~~~~~~~~~~~^~~
foo.cc:24:27: warning: unused variable ‘w’ [-Wunused-variable]
   24 |                         T w=q.top().first;
      |                           ^