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

Analysis:

Two pointers to check if each pointer char is the same.

class Solution(object):
 def isPalindrome(self, s):
 “””
 :type s: str
 :rtype: bool
 “””
 if not s: return True
 i, j = 0, len(s)-1
 
 while i < j:
   while i < j and not s[i].isalnum():
     i += 1
   while i < j and not s[j].isalnum():
     j -= 1
 
   if s[i].lower()!=s[j].lower():
     return False
   i += 1
   j -= 1
 
 return True