multiplyVectorByInteger.cpp

    vector<int> multiplyVectorByInteger(const vector<int>& numVector, int n) {
      vector<int> returnVec(numVector.size());
      
      int carry = 0;
      
      for (int i = 0; i < numVector.size(); ++i) {
        returnVec[i] = (numVector[i]*n + carry) % 10;
        carry = (numVector[i]*n + carry) / 10;
      }
      
      while (carry) {
        returnVec.push_back(carry%10);
        carry /= 10;
      }
      
      return returnVec;
    }


    int main() {
        vector<int> output = {1};
        int n;
        cin >> n;
        //....
        while (n) {
          output = multiplyVectorByInteger(output, n);
          n--;
        }
        
        //....
    }