258. Add Digits



Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.

For example:

Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only one digit, return it

public class Solution {    public int addDigits(int num) {        while(num>=10)        {            num = (num/10)+num%10;          }          return num;      }}

public int addDigits(int num) {          return 1 + (num-1)%9; //num先-1，后又加1是为了避免可以整除9的情况出现，此时为0，而相加不可能出现和为0的情况     }