leetcode 258. Add Digits

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258. Add Digits

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Question

Total Accepted: 68661 Total Submissions: 142851 Difficulty: Easy

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?

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Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

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思维题，找找规律，详见代码：

class Solution {
public:
int addDigits(int num) {
if(num <= 9){
return num;
}
else{
if(num % 9 == 0){
return 9;
}
else{
return num % 9;
}
}
}
};