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9. Palindrome Number

Math

Problem - Palindrome Number

Easy

Given an integer x, return true if x is a palindrome, and false otherwise.

 

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?

Solutions

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public class Solution {
    public bool IsPalindrome(int x) {
        // Negative numbers and numbers ending with 0 (except 0 itself) cannot be palindromes
        if (x < 0 || (x != 0 && x % 10 == 0)) {
            return false;
        }

        int reversed = 0;
        int original = x;

        while (x > reversed) {
            reversed = reversed * 10 + x % 10;
            x /= 10;
        }
        return x == reversed || x == reversed / 10;
    }
}

Submission Stats:

  • Runtime: 50 ms (5.05%)
  • Memory: 31.6 MB (100.00%)
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import math

class Solution:
    def isPalindrome(self, x: int) -> bool:
        if x < 0 or (x % 10 == 0 and x != 0):
            return False

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

        return reversed_half_x == x or reversed_half_x//10 == x

Submission Stats:

  • Runtime: 9 ms (44.00%)
  • Memory: 17.9 MB (19.98%)