989. Add to Array-Form of Integer

For a non-negative integer X, the array-form of X is an array of its digits in left to right order. For example, if X = 1231, then the array form is [1,2,3,1].

Given the array-form A of a non-negative integer X, return the array-form of the integer X+K.

Example 1:

Input: A = [1,2,0,0], K = 34
Output: [1,2,3,4]
Explanation: 1200 + 34 = 1234

Example 2:

Input: A = [2,7,4], K = 181
Output: [4,5,5]
Explanation: 274 + 181 = 455

Example 3:

Input: A = [2,1,5], K = 806
Output: [1,0,2,1]
Explanation: 215 + 806 = 1021

Example 4:

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

Note：

1. 1 <= A.length <= 10000

2. 0 <= A[i] <= 9

3. 0 <= K <= 10000

4. If A.length > 1, then A[0] != 0

vector<int> addToArrayForm(vector<int>& A, int K) {
    int n = A.size(), carry = K;
    vector<int> res(A.begin(), A.end());
    for (int i = n - 1; i >= 0; --i) {
        int tmp = (i >= 0 ? A[i] : 0) + carry;
        res[i] = tmp % 10;
        carry = tmp / 10;
    }
    while (carry) {
        res.insert(res.begin(), carry % 10);
        carry /= 10;
    }
    return res;
}