Two Pointers:- Valid Palindrome

 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.

Solution:

Reverse String in python: [::-1]

Check if character is alpha numeric(to avoid " , "): .isalnum()

class Solution:

def isPalindrome(self, s: str) -> bool:

new=""

for c in s:

if c.isalnum():

new += c.lower()

return new == new[::-1]

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