In file included from /usr/include/c++/6/cassert:44:0,
                 from /in/foo.cc:20:
/in/foo.cc: In function 'int query(int, int)':
/in/foo.cc:155:42: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     assert(len[top]-(k-(dep[x]-dep[top]))<sav[top].size());
            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~