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258. Add Digits

Difficulty Topics

Description

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

 

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

 

Constraints:

  • 0 <= num <= 231 - 1

 

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

Solution

add-digits.py
class Solution:
    def addDigits(self, num: int) -> int:

        while num >= 10:
            s = 0

            while num > 0:
                s += num % 10
                num //= 10

            num = s

        return num