验证回文串

class Solution:
    def isPalindrome(self, s: str) -> bool:
        s = s.lower()
        
        i = 0
        j = len(s) - 1
        string = "abcdefghijklmnopqrstuvwxyz0123456789"
        while(i < j):
            if not(s[i].isalpha() or s[i].isdigit()):
                i += 1
            elif not(s[j].isalpha() or s[j].isdigit()):
                j -= 1
            else:
                if s[i] != s[j]:
                    return False
                else:
                    i += 1
                    j -= 1
        
        return True
            

双指针法，没办法，不如a == a[::-1]好用