258. 各位相加

https://leetcode-cn.com/problems/add-digits/

使用递归就行

class Solution {
    public int addDigits(int num) {
        if(num < 10) return num;
        int next = 0;
        while(num != 0){
            next = next + num % 10;
            num /= 10;
        }
        return addDigits(next);
    }
}