Write a function that checks if a given string is a valid palindrome. A palindrome is a word, phrase, number, or other sequences of characters that reads the same forward and backward (ignoring spaces, punctuation, and capitalization).

Input: "A man, a plan, a canal: Panama"
Output: true
Explanation: After removing all non-alphanumeric characters and converting everything to the same case, the string becomes "amanaplanacanalpanama", which is a palindrome.

Requirements:

• The function signature should be bool isPalindrome(string s).
• The solution must handle empty strings and strings with only one character.

Follow-up Discussion:

• How would you optimize your solution for long strings?
• What edge cases can you think of, and how does your function address them?