Valid Palindrome

Problem Statement

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.

Leetcode Link

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.

Code

Python Code

import re
class Solution:
    def isPalindrome(self, s: str) -> bool:
        # clean up the string first
        s = re.sub("[^a-z0-9]", "", s.lower())
        # is it the same as its reverse?
        return s == s[::-1]