LeetCode - Add Digits

Question

Link:https://leetcode.com/problems/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.

Follow up:

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

Code

一个比较挫的用到了循环和递归的算法。（C++ : 8ms）

class Solution {
public:
int addDigits(int num) {
if(num < 10)
return num;

int digit = 0;
while (num > 0){
digit += (num % 10);
num /= 10;
}

return addDigits(digit);
}
};

What the fuck!这玩意一行代码就可以解决了！

看个高级版本的。。。原理百度你就知道了。。。

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