foo.cc: In function 'void dfs(int, int)':
foo.cc:25:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<e[x].size();i++)
              ~^~~~~~~~~~~~
foo.cc: In function 'void dfs2(int, int)':
foo.cc:66:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(i==e[x].size()-1)
       ~^~~~~~~~~~~~~~~