> For the complete documentation index, see [llms.txt](https://liuyang89116.gitbook.io/my-leetcode-book/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://liuyang89116.gitbook.io/my-leetcode-book/post_chapter_2_math/problem_7_reverse_integer.md).

# Problem 7: Reverse Integer

> <https://leetcode.com/problems/reverse-integer/>

## 思路

* 数学类的翻转通常都不是为了转化成 String 数组，而是通过数学的公式得出翻转的结果
* 公式&#x20;

  ```
  reverseNum = reverseNum * 10 + x % 10;
  x = x / 10;
  ```

```java
public class Solution {
    public int reverse(int x) {
        if (x == 0) {
            return 0;
        }

        int reverseNum = 0;
        while (x != 0) {
            int temp = reverseNum * 10 + x % 10;
            x /= 10;
            if (temp /10 != reverseNum) {
                return 0;
            }
            reverseNum = temp;
        }
        return reverseNum;
    }
}
```

## 易错点

1. 数据溢出

   ```java
   if (temp /10 != reverseNum) {
            return 0;
   }
   ```

   当 reverseNum 足够大的时候，再乘以 10 就会数据溢出。所以在这里需要 check