[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;
}
};