125. Valid Palindrome

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.

Given a string s, return true if it is a palindrome, or false otherwise.

Example 1:

Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.

Example 2:

Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.

Example 3:

Input: s = " "
Output: true
Explanation: s is an empty string "" after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.

Constraints:

• 1 <= s.length <= 2 * 105
• s consists only of printable ASCII characters.

Accepted

1,181,069

Submissions

2,868,121

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