Palindrome Number — LeetCode 9 Python Solution

The problem

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

Example

Input

x = 121

Output

true

Explanation

121 reads as 121 from left to right and from right to left.

Python solution

class Solution:
    def isPalindrome(self, x: int) -> bool:
        if x < 0 or (x and x % 10 == 0):
            return False
        y = 0
        while y < x:
            y = y * 10 + x % 10
            x //= 10
        return x in (y, y // 10)

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 9. Palindrome Number is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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