/in/foo.cc: In function 'bool spfa(long long int)':
/in/foo.cc:25:26: 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]
   25 |         for(int i = 0; i < vec[u].size(); i++) {
      |                        ~~^~~~~~~~~~~~~~~