> For the complete documentation index, see [llms.txt](https://anand-aryan.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://anand-aryan.gitbook.io/leetcode/258.-add-digits.md).

# 258. Add Digits

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?

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

## Solution <a href="#solution" id="solution"></a>

```java
public class Solution {
    public int addDigits(int num) {
        if (num == 0) return 0;
        return (num-1) % 9 + 1;
    }
}
```