foo.cc: In function 'void dfs(int, int)':
foo.cc:10:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0; i<t[x].size(); i++)
                ~^~~~~~~~~~~~
foo.cc: In function 'void hsh(int, int, int, int)':
foo.cc:20:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0; i<t[x].size(); i++)
                ~^~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:44:18: error: too few arguments to function 'void hsh(int, int, int, int)'
   hsh(i, root, -1);
                  ^
foo.cc:17:6: note: declared here
 void hsh(int id, int x, int fa, int rt)
      ^~~
foo.cc:61:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int j=0; j<cnt[i].size()-1; j++) cout<<cnt[i][j]<<"=";
                  ~^~~~~~~~~~~~~~~~

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