foo.cc: In function 'int query(int, int, int)':
foo.cc:48:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0;i < pre.size();++i) {
                    ~~^~~~~~~~~~~~
foo.cc:55:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0;i < pre.size();++i) {
                    ~~^~~~~~~~~~~~
foo.cc:44:9: warning: unused variable 'cnt' [-Wunused-variable]
     int cnt = 0,pos = 0;
         ^~~
foo.cc:44:17: warning: unused variable 'pos' [-Wunused-variable]
     int cnt = 0,pos = 0;
                 ^~~
foo.cc: In function 'int main()':
foo.cc:84:24: warning: format '%lld' expects argument of type 'long long int', but argument 2 has type 'int' [-Wformat=]
     printf("%lld\n",ans);
                        ^