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125. Valid Palindrome

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 

Solutions (Python)

1. Two Pointers

classSolution: defisPalindrome(self, s: str) ->bool: s=''.join([cforcinsifc.isalnum()]).lower() i, j=0, len(s) -1whilei<j: ifs[i] !=s[j]: returnFalsei+=1j-=1returnTrue

2. Reverse

classSolution: defisPalindrome(self, s: str) ->bool: s=''.join([cforcinsifc.isalnum()]).lower() returns[::-1] ==s