/in/foo.cc: In function 'void prim()':
/in/foo.cc:29:31: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<edge>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   29 |                 for (int i=0;i<g[k.v].size();i++)
      |                              ~^~~~~~~~~~~~~~