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 <= A.length <= 10000

0 <= A[i] <= 9

0 <= K <= 10000

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

难度：easy

题目：非负整数Ｘ的数组表示形式为一个单数字数组且顺序由左到右。例如，Ｘ＝1231,数组表示为［1,2,3,1]。

给定数字Ｘ的数组表示形式Ａ，返回Ｘ＋Ｋ的数组表示形式。

思路：从右向左加法运算

Runtime: 11 ms, faster than 91.55% of Java online submissions for Add to Array-Form of Integer.

Memory Usage: 41.8 MB, less than 75.63% of Java online submissions for Add to Array-Form of Integer.

class Solution {
    public List<Integer> addToArrayForm(int[] A, int K) {
        List<Integer> result = new ArrayList<>();
        int carry = 0, t = 0, n = A.length;
        while (--n >= 0 || K > 0) {
            t = n >= 0 ? A[n] + K % 10 + carry: K % 10 + carry;
            carry = t / 10;
            result.add(t % 10);
            K /= 10;
        }
        if (carry > 0) {
            result.add(carry);
        }
        Collections.reverse(result);
        
        return result;
    }
}