LeetCode 989. 数组形式的整数加法

示例 1：
输入：A = [1,2,0,0], K = 34
输出：[1,2,3,4]
解释：1200 + 34 = 1234

示例 2：
输入：A = [2,7,4], K = 181
输出：[4,5,5]
解释：274 + 181 = 455

示例 3：
输入：A = [2,1,5], K = 806
输出：[1,0,2,1]
解释：215 + 806 = 1021

示例 4：
输入：A = [9,9,9,9,9,9,9,9,9,9], K = 1
输出：[1,0,0,0,0,0,0,0,0,0,0]
解释：9999999999 + 1 = 10000000000
 
提示：
1 <= A.length <= 10000
0 <= A[i] <= 9
0 <= K <= 10000
如果 A.length > 1，那么 A[0] != 0

class Solution {
public:
    vector<int> addToArrayForm(vector<int>& A, int K) {
        int bit, i, n = A.size(), carry = 0, sum;
        for(i = n-1; i >= 0 && K; --i)
        {
        	bit = K%10;//K的低位上的数
        	K /= 10;
        	sum = A[i]+bit+carry;
        	A[i] = sum%10;
        	carry = sum/10;//进位
        }
        if(K == 0)//K加完了，处理进位
        {
        	while(i >= 0)
        	{
        		if(carry == 0)
        			break;
        		sum = A[i]+carry;
	        	A[i] = sum%10;
	        	carry = sum/10;
	        	i--;
        	}
        	if(i == -1 && carry)
        		A.insert(A.begin(),carry);
        }
        else//K不为0，数组遍历完了
        {
        	while(K || carry)
        	{
        		bit = K%10;
        		K /= 10;
        		sum = bit+carry;
        		carry = sum/10;
        		A.insert(A.begin(),sum%10);
        	}
        }
        return A;
    }
};