/in/foo.cc: In function 'int dfs(std::vector<int>&, int, int)':
/in/foo.cc:13:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0; i<V.size(); i++)
           ~^~~~~~~~~
/in/foo.cc:16:6: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if(i<V.size() && V[i]==x) 
     ~^~~~~~~~~