/in/foo.cc: In function 'void tarjan(int)':
/in/foo.cc:18:18: 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 dfs(int, int)':
/in/foo.cc:53:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<nG[u].size();i++)
                 ~^~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:84:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0;i<G[u].size();i++)
                     ~^~~~~~~~~~~~