README.md

125. Valid Palindrome

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:

Input: "race a car"
Output: false

Solutions (Python)

1. Two Pointers

class Solution:
    def isPalindrome(self, s: str) -> bool:
        s = ''.join([c for c in s if c.isalnum()]).lower()
        i, j = 0, len(s) - 1
        while i < j:
            if s[i] != s[j]:
                return False
            i += 1
            j -= 1
        return True

2. Reverse

class Solution:
    def isPalindrome(self, s: str) -> bool:
        s = ''.join([c for c in s if c.isalnum()]).lower()
        return s[::-1] == s