vector<int> multiply(vector<int>& a, vector<int>& b) {
  int m = a.size(), n = b.size();
  vector<int> c(m + n, 0);

  // 逐位相乘，逆序存储
  for (int i = 0; i < m; i++) {
    for (int j = 0; j < n; j++) {
      c[i + j] += a[i] * b[j];
    }
  }

  // 处理进位
  int carry = 0;
  for (int k = 0; k < c.size(); ++k) {
    ________________________________ // 在此处填入代码
    c[k] = temp % 10;
    carry = temp / 10;
  }

  while (c.size() > 1 && c.back() == 0)
    c.pop_back();
  return c;
}