LeetCode 125 - Valid Palindrome - 2023.10.07 solution

class Solution:
    def isPalindrome(self, s: str) -> bool:
        """ Proposed solution: convert the string to lowercase, then have two pointers
        step inwards from the outside.
        """
        s = s.lower()

        # Have them start outside of the range of the word so that I don't need to consider the
        # first iteration as a special case.
        l = -1
        r = len(s)
        while l < r:
            l += 1
            r -= 1

            # have them step inwards until they're both on a new character
            # I need to consider
            while l < r and not s[l].isalnum():
                l += 1
            while r > l and not s[r].isalnum():
                r -= 1

            # compare them
            if s[l] != s[r]:
                return False
        return True