[每日 LeetCode] 989. Add to Array-Form of Integer

Description:

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

思路：本题的意思要把数组中的元素当做整数，并将此整数加上 K 后的整数转化为新的数组。考虑首先把数组逆序，然后提取整数 K 的各位上的数分别和数组中的元素相加，注意判断是否有进位，操作完成后再逆序输出。

C++ 代码

class Solution {
public:
    vector<int> addToArrayForm(vector<int>& A, int K) {
    reverse(A.begin(), A.end());
    for (int i = 0; i < A.size(); i++) {
        A[i] += K;
        K = A[i] / 10;
        A[i] %= 10;
    }
    while (K) {
        A.push_back(K%10);
        K /= 10;
    }
    reverse(A.begin(), A.end());
    return A;
    }
};
​

运行时间：116ms

运行内存：12.4M