/in/foo.cc: In function 'void spfa()':
/in/foo.cc:21:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0; i<q.size(); i++) {
                ~^~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:52:21: error: 'n' was not declared in this scope
   std::cout << dist[n - 1] << std::endl;
                     ^