輸入：num = [1,2,0,0], k = 34
輸出：[1,2,3,4]
解釋：1200 + 34 = 1234

輸入：num = [2,7,4], k = 181
輸出：[4,5,5]
解釋：274 + 181 = 455

輸入：num = [2,1,5], k = 806
輸出：[1,0,2,1]
解釋：215 + 806 = 1021

class Solution {
public:
    vector<int> addToArrayForm(vector<int>& num, int k) {
        vector<int> ans(num.size());
        int index = num.size()-1;
        int carry = 0;
        int sum = 0;
        while(k > 0 && index >= 0){
            sum = carry + num[index] + k%10;
            ans[index] = sum%10;
            carry = sum/10;
            k /= 10;
            index -= 1;
        }
        while(index >= 0){
            sum = carry + num[index];
            ans[index] = sum%10;
            carry = sum/10;
            index -= 1;
        }
        vector<int> kitem;
        while(k > 0){
            sum = carry + k%10;
            kitem.emplace_back(sum%10);
            carry = sum/10;
            k /= 10;
        }
        if(kitem.size() > 0 || carry > 0){
            reverse(kitem.begin(), kitem.end());
            kitem.insert(kitem.end(), ans.begin(), ans.end());
            if(carry > 0){
                vector<int> temp(1, carry);
                temp.insert(temp.end(), kitem.begin(), kitem.end());
                return temp;
            }
            else{
                return kitem;
            }
        }
        return ans;
    }
};