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# 題目敘述

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

# Solution

class Solution {
public:
    int addDigits(int num) {
        int res = num;
        while (num > 9) {
            res = 0;
            while (num != 0) {
                res += num % 10;
                num /= 10;
            }
            num = res;
        }
        return res;
    }
};
class Solution {
    public int addDigits(int num) {
        int res = num;
        while (num > 9) {
            res = 0;
            while (num != 0) {
                res += num % 10;
                num /= 10;
            }
            num = res;
        }
        return res;
    }
}
class Solution:
    def addDigits(self, num: int) -> int:
        res = num
        while num > 9:
            res = 0
            while num != 0:
                res += num % 10
                num //= 10
            num = res
        return res