[LeetCode] Add Digits

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.

For example:

Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only one digit, return it.

 

分析一：最简单的循环方法

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

 

分析二：参考https://leetcode.com/discuss/52122/accepted-time-space-line-solution-with-detail-explanations

class Solution {
public:
    int addDigits(int num) {
        return 1 + (num - 1) % 9;
    }
};