Simplify Complexities

class Solution(object):
    def isPalindrome(self, s):
        """
        :type s: str
        :rtype: bool
        """
        if len(s) < 1:
            return True
        
        start, end = 0, len(s) - 1
        
        while start < end:
            # Loop till a special char is found
            while start < end and not s[start].isalnum():
                start += 1
                
            # Always keep the check start < end
            while start < end and not s[end].isalnum():
                end -= 1
            
            # For a pure non-alnum string e.g. "..", start = end = 1
            # The next iteration will have start +=1 => 2
            # So breaking the loop correctly.
            
            if s[start].lower() != s[end].lower():
                return False
            
            start += 1
            end -= 1
            
        return True

Reference

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

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