Method normalize

Math/Subset Sum Problem.cpp:137–139

struct poly {
  vector<mint> a;
  inline void normalize() {
    while((int)a.size() && a.back() == 0) a.pop_back();
  }
  template<class...Args> poly(Args...args): a(args...) { }
  poly(const initializer_list<mint> &x): a(x.begin(), x.end()) { }
  int size() const { return (int)a.size(); }