/in/foo.cc: In function 'void prebfs()':
/in/foo.cc:51:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<e[x].size();i++)
               ~^~~~~~~~~~~~
/in/foo.cc: In function 'void bfs()':
/in/foo.cc:73:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<e[x].size();i++)
               ~^~~~~~~~~~~~