foo.cc: In function ‘void spfa(int)’:
foo.cc:15:31: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   15 |                 for(int i=0; i<v[t].size(); i++){
      |                              ~^~~~~~~~~~~~