125. Valid Palindrome - two pointers

125. Valid Palindrome

Easy

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

Accepted 500,090 Submissions 1,458,933

Double pointer

class Solution:
    def isPalindrome(self, s: str) -> bool:
        if len(s) <= 1:
            return True
        
        s = s.upper()
        l = 0
        r = len(s) - 1
        
        while l<r:
            if not s[l].isalnum():
                l += 1
            elif not s[r].isalnum():
                r -= 1
            elif s[l] != s[r]:
                return False
            else:
                l += 1
                r -= 1
        
        return True

PS：

Python string determination

Python isX string method

1.isupper()

If the string has at least one letter, and all letters are capitalized, isupper () method returns a Boolean value True.

2.islower()

If there is at least one letter string, and all the letters are in lowercase, islower () method returns a boolean value True.

3kislf ()

If the string contains only letters, and the non-empty, return True.

4.isalnum ()

If the string contains only alphanumeric characters, and non-empty, return True.

5.isdecimal ()

If the string contains only numeric characters, and is non-empty, returns True.

6.isspace()

If the string contains only spaces, tabs and line feed, and non-empty, return True.

7.istitl A ()

If the string contains only begin with a capital letter followed by lowercase letters are the words, return
True. ----------------
Copyright: This article is CSDN blogger "guloutingfengyu" original article, follow the CC 4.0 BY-SA copyright agreement, reproduced, please attach the original source link and this statement.
Original link: https: //blog.csdn.net/guloutingfengyu/article/details/80089190