/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:18:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < G[u].size(); i++) {
                 ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:61:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = 0; j < G[i].size(); j++){
                   ~~^~~~~~~~~~~~~