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?
看题目意思,肯定是有规律可循了,写下几个数字 找出规律
class Solution {
public:
int addDigits(int num) {
if(num<10)return num;
num%=9;
if(num ==0 )return 9;
return num;
}
};
知识点是 Digital root https://en.wikipedia.org/wiki/Digital_root