9. Palindrome Number - leetcode - easy - python

 

9. Palindrome Number

Example 1:

Input: x = 121
Output: true
Explanation: 121 reads as 121 from left to right and from right to left.

Example 2:

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

 

Constraints:

• -231 <= x <= 231 - 1

 

Follow up: Could you solve it without converting the integer to a string?

class Solution:

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

        if x < 0:

            return False

        rev = 0

        n = x

        while n:

            rev = rev * 10 + n % 10

            n //= 10

        return x == rev

Explanation (Simple Version)

1. Negative numbers → not a palindrome.

2. Reverse the number using rev = rev * 10 + last_digit.

3. Compare reversed number with original → True if same, False otherwise.