Given a string `s`, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. Return `true` if it is a palindrome, or `false` otherwise.
s = input string
true if s is a palindrome ignoring non-alphanumeric characters, false otherwise
Example 1:
Input:
s = "A man, a plan, a canal: Panama"
Output:
true
Explanation:
Ignoring punctuation and case, it reads 'amanaplanacanalpanama' which 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:
Empty string is a valid palindrome.