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?
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
观察发现 out = (in - 1) % 9 + 1
Complexity
时间复杂度 O(1),空间复杂度 O(1)
Code
public class Solution {
public int addDigits(int num) {
if (num == 0)
return 0;
return (num - 1) % 9 + 1;
}
}