foo.cc: In function 'void DFS(int, int&, int)':
foo.cc:54:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < Gmap[x].size(); i++)
                   ~~^~~~~~~~~~~~~~~~
foo.cc:61:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < Gmap[x].size(); i++)
                   ~~^~~~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。