Math
Simulation
Number Theory
Given an integer num, repeatedly add all its digits until the result has only one digit, and return it.
Examples
Example 1
Input: num = 38
Output: 2
Explanation: The process is
38 --> 3 + 8 --> 11
11 --> 1 + 1 --> 2
Since 2 has only one digit, return it.
Example 2
Input: num = 0
Output: 0
Follow Up
- Could you do it without any loop/recursion in O(1) runtime?