Valid Palindrome

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

For example, "A man, a plan, a canal: Panama" is a palindrome. "race a car" is not a palindrome.

Note: Have you consider that the string might be empty? This is a good question to ask during an interview.

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

URL: https://leetcode.com/problems/valid-palindrome/

import re
class Solution:
    # @param {string} s
    # @return {boolean}
    def isPalindrome(self, s):
        if len(s) == 0:
            return True
        else:
            start = 0
            s = s.lower()
            newS = re.sub(r"[^a-zA-Z0-9]","",s)
            end = len(newS)-1
            while start < end:
                if newS[start] == newS[end]:
                    start = start + 1
                    end = end - 1
                else:
                    return False
            return True