AddtoArray-FormofInteger*

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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.

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class Solution {
  public:
    vector<int> addToArrayForm(vector<int> &A, int k) {
        vector<int> ans;
        for (int carry = 0, i = A.size() - 1; i >= 0 || k != 0 || carry != 0; --i, k /= 10) {
            if (i >= 0) carry += A[i];
            if (k != 0) carry += k % 10;
            ans.push_back(carry % 10);
            carry /= 10;
        }
        reverse(ans.begin(), ans.end());
        return ans;
    }
};