LeetCode 125 - Valid Palindrome - 2023.04.01 solution

class Solution:
    def isPalindrome(self, s: str) -> bool:
        """ Have two pointers step inwards, comparing the character at each index.
        """
        l = -1
        r = len(s)

        while l < r:
            l += 1
            while l < len(s) and not s[l].lower().isalnum():
                l += 1

            r -= 1
            while r >= 0 and not s[r].lower().isalnum():
                r -= 1

            if l >= len(s) and r >= 0:
                return False
            if r < 0 and l < len(s):
                return False
            if l >= len(s) and r < 0:
                return True

            if s[l].lower() != s[r].lower():
                return False

        return True