Adding digits with O(1) complexity

0258-Add-Digits.py

@@ -0,0 +1,18 @@
+'''
+Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.
+
+Example:
+
+Input: 38
+Output: 2 
+Explanation: 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?
+'''
+class Solution:
+    def addDigits(self, num: int) -> int:
+        if num < 10:
+            return num
+        return num % 9 if num % 9 != 0 else 9