Example 1:

Input: A = [1,2,0,0], K = 34

Output: [1,2,3,4]

Explanation: 1200 + 34 = 1234

Input: A = [2,7,4], K = 181

Output: [4,5,5]

Explanation: 274 + 181 = 455

Input: A = [2,1,5], K = 806

Output: [1,0,2,1]

Explanation: 215 + 806 = 1021

Input: A = [9,9,9,9,9,9,9,9,9,9], K = 1

Output: [1,0,0,0,0,0,0,0,0,0,0]

Explanation: 9999999999 + 1 = 10000000000

class Solution {

public:

    vector<int> addToArrayForm(vector<int>& A, int K) {

        int n = A.size();

        vector<int> ans;

        string words1 = toString(K), words2 = "";

        for(int i = 0; i < n; i ++)

            words2 += ('0' + A[i]);

        string sum = addStrings(words1, words2);

        for(int i = 0; i < sum.length(); i ++)

            ans.push_back(sum[i] - '0');

        return ans;

    }

    string toString(int x) {

        string s = "";

        while(x) {

            s += (x % 10) + '0';

            x /= 10;

        }

        for(int i = 0; i < s.length() / 2; i ++)

            swap(s[i], s[s.length() - i - 1]);

        return s;

    }

    string addStrings(string num1, string num2) {

        string c = "";

        int len1 = num1.length();

        int len2 = num2.length();

        int len = max(len1, len2);

        for(int i = len1; i < len; i ++)

            num1 = "0" + num1;

        for(int i = len2; i < len; i ++)

            num2 = "0" + num2;

        int ok = 0;

        for(int i = len - 1; i >= 0; i --) {

            char temp = num1[i] + num2[i] - '0' + ok;

            if(temp > '9') {

                ok = 1;

                temp -= 10;

            }

            else ok = 0;

            c = temp + c;

        }

        if(ok) c = "1" + c;

        return c;

    }

};