View Compilation Error

0_0_26479796_25599.cpp: In function 'void mul(std::vector<long long int>&, std::vector<long long int>&)':
0_0_26479796_25599.cpp:72:26: error: request for member 'resize' in 'x1', which is of non-class type 'll [200018] {aka long long int [200018]}'
     ntt(x1, len, -1); x1.resize(sz1+sz2-1,0);
                          ^