/in/foo.cc: In function 'bool spfa(long long int)':
/in/foo.cc:17:30: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |                 for(int i=0;i<vec[u].size();i++){
      |                             ~^~~~~~~~~~~~~~