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?
Could you do it without any loop/recursion in O(1) runtime?
Hint:
- A naive implementation of the above process is trivial. Could you come up with other methods?
- What are all the possible results?
- How do they occur, periodically or randomly?
- You may find this Wikipedia article useful.
Solution 1: it is repeat every 9 nums.
public class Solution {
public int addDigits(int num) {
if (num==0) return 0;
int k=num%9;
return k==0?9:k;
}
}
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