/in/foo.cc: In function 'void bfs()':
/in/foo.cc:24:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i=0; i<e[f].size(); ++i) {
                 ~^~~~~~~~~~~~
/in/foo.cc:31:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i=0; i<e[f].size(); ++i) {
                 ~^~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:65:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0; i<ans.size(); ++i)
                ~^~~~~~~~~~~