<LeetCode><Easy>258Add 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.

Follow up:

Could you do it without any loop/recursion in O(1) runtime?

#Python2   80ms

class Solution(object):
def addDigits(self, num):
add=lambda x:sum(int(i) for i in str(x))
s=add(num)
while 1:
if s<10:return s
else:s=add(s)

#Python2  64ms

class Solution(object):
def addDigits(self, num):
while num>9:
num=sum(int(i) for i in str(num))
return num