Problem Statement

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.

Given a string s, return true if it is a palindrome, or false otherwise.

Example 1:

Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.

Example 2:

Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.

Example 3:

Input: s = " "
Output: true
Explanation: s is an empty string "" after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.



class Solution:
    def isPalindrome(self, s: str) -> bool:
            T: O(N)
            S: O(N)
        # Create a new list that only has letters and numbers
        values = [ch.lower() for ch in s if s.isalnum()]
        # Initialize two pointers
        a, b = 0, len(values) - 1

        # Walk from the front and back to try to find a
        # pair that is not equal. Return False if such a
        # is found.
        while a < b:
            if values[a] != values[b]:
                return False

            a += 1
            b -= 1

        # The string is a valid palindrome. Return True
        return True