## Question

Given an integer `num`

, repeatedly add all its digits until the result has only one digit, and return it.

**Example 1:**

Input:num = 38Output:2Explanation:The process is 38 --> 3 + 8 --> 11 11 --> 1 + 1 --> 2 Since 2 has only one digit, return it.

**Example 2:**

Input:num = 0Output:0

**Constraints:**

`0 <= num <= 2`

^{31}- 1

**Follow up:** Could you do it without any loop/recursion in `O(1)`

runtime?

## Python Solution

class Solution: def addDigits(self, n: int) -> int: if n==0: return 0 if n%9==0: return 9 else: return n%9