> For the complete documentation index, see [llms.txt](https://timmybeeflin.gitbook.io/cracking-leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://timmybeeflin.gitbook.io/cracking-leetcode/math/7.-reverse-integer.md).

# 7. Reverse Integer

![](/files/-MeOWoBl0lhrYv1dAqze)

![](/files/-MeOWyAN5ubdL1nzKf9f)

Remembering the formula:

```
res = res*10 + x%10 (remainder)
x /=10
```

notice the boundary

time: O(n)

space: O(1)

```java
class Solution {
    public int reverse(int x) {
        long res = 0;
        while (x != 0) {
            res = res*10 + x%10;
            x /= 10;
            if (res > Integer.MAX_VALUE || res < Integer.MIN_VALUE) return 0;
        }
        return (int)res;
    }
}
```