foo.cc: In function 'int query(int, int, int)':
foo.cc:47:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0;i < pre.size();++i) {
                    ~~^~~~~~~~~~~~
foo.cc:54:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0;i < pre.size();++i) {
                    ~~^~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:62:17: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long long int' [-Wformat=]
  printf("%d\n",n);
                 ^