Palindrome String

Palindromic Substrings

Longest Common Prefix

Determine whether a phrase reads the same after ignoring case and non-alphanumeric characters.

Determine whether `s` is a palindrome after removing every non-alphanumeric character and comparing letters without regard to case.

**Input / output**
- Input: `s: string`
- Output: boolean

**Examples**
1. `"A man, a plan, a canal: Panama"` returns `true`.
2. `"race a car"` returns `false`.

**Constraints**
- `0 <= s.length <= 200,000`
- Alphanumeric means the ASCII ranges `A-Z`, `a-z`, and `0-9`.

**Follow-up**
Can you solve it with two pointers and constant auxiliary space instead of building a cleaned copy?

- The task is to determine if a given string is a palindrome.
- Ignore non-alphanumeric characters, and treat upper- and lower-case letters as the same.
- The goal is to avoid extra storage, so we'll use character-by-character comparison instead of storing a reversed string.

Understanding the Problem

- Use a two-pointer technique, one starting from the beginning and one from the end of the string.
- Increment the left pointer and decrement the right pointer after each comparison.

Use Two Pointers to Compare Characters

- As you move the two pointers, skip any characters that are not alphanumeric (like spaces, punctuation).
- Use Python's `isalnum()` method to check if a character is alphanumeric.

Skip Non-Alphanumeric Characters

- Compare the characters at the left and right pointers, ignoring case.
- If the characters are not equal, the string is not a palindrome and you can return `False` immediately.

Compare Characters (Ignore Case)

- If all characters match as you move the pointers, the string is a palindrome.
- Once the two pointers meet or cross, return `True` to indicate the string is a palindrome.

Return the Result

- Consider edge cases like an empty string or a string containing only non-alphanumeric characters.
- These should return `True` since they can be considered palindromes.