foo.cc: In function ‘int main()’:
foo.cc:24:34: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   24 |                 for(int i = 0; i < g[u].size(); i++){
      |                                ~~^~~~~~~~~~~~~