LeetCode258. Add Digits

一、题目

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?

二、题解

class Solution {
public:
    int addDigits(int num) {
        while(num > 9){
            int sum = 0;
            while(num){
                sum += num % 10;
                num /= 10;
            }
            num = sum;
        }
        return num;
    }
};