题目
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.
解题思路
和普通的判断字符串是否为回文一样，l r两个指针，每次在比较之前，先跳掉所有非字母或数字的字符
代码
class Solution:
def isPalindrome(self, s: str) -> bool:
l, r = 0, len(s) - 1
while l < r:
while l < r and not s[l].isalnum():
l += 1
while l < r and not s[r].isalnum():
r -= 1
if l < r:
if s[l].lower() != s[r].lower():
return False
l += 1
r -= 1
return True
