# LeetCode 9. Palindrome Number

## Description

https://leetcode.com/problems/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.
```

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

## Explanation

Negative numbers are not palindrome numbers, e.g., -121. We can exclude negative numbers first.

Then by comparing the integer number and its reversed integer, we can determine whether the integer is a palindrome.

## Java Solution

```public class Solution {
public boolean isPalindrome(int x) {
if (x < 0 || x != 0 && x % 10 == 0) {
return false;
}

// reverse process
int reversed = 0;
int original = x;
while (x != 0) {
reversed = reversed * 10 + x % 10;
x = x / 10;
}

return reversed == original;
}
}```

## Python Solution

``````class Solution:
def isPalindrome(self, x: int) -> bool:

if x < 0:
return False

reverse = 0
original = x

while x > 0:
reverse = reverse * 10 + x % 10
x = x // 10

return reverse == original``````
• Time complexity: O(N)
• Space complexity: O(1)