> For the complete documentation index, see [llms.txt](https://jimmylin1991.gitbook.io/practice-of-algorithm-problems/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jimmylin1991.gitbook.io/practice-of-algorithm-problems/math/9.-palindrome-number.md).

# 9. Palindrome Number

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

**Example 1:**

```
Input: 121
Output: true
```

**Example 2:**

```
Input: -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.
```

**Example 3:**

```
Input: 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.
```

**Follow up:**

Coud you solve it without converting the integer to a string?

```cpp
bool isPalindrome(int x) { // time: O(logx); space: O(1)
    if (x < 0) return false;
    int orig = x;
    long num = 0;
    while (x) {
        num = num * 10 + x % 10;
        x /= 10;
    }
    return orig == num;
}
```