class Solution:

    def check_alphabet(self, s: str):
        if ord(s) >= ord('a') and ord(s) <= ord('z'):
            return True
        if ord(s) >= ord('A') and ord(s) <= ord('Z'):
            return True
        if ord(s) >= ord('0') and ord(s) <= ord('9'):
            return True
        return False

    def isPalindrome(self, s: str) -> bool:

        # remove special characters
        left = 0
        right = len(s) - 1

        while(left < right):

            while(left < len(s) and not self.check_alphabet(s[left])):
                left += 1

            while(right >= 0  and not self.check_alphabet(s[right])):
                right -= 1

            if left > right:
                break

            if s[left].lower() != s[right].lower():
                return False

            left += 1
            right += -1

        return True