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;
                 ^~~