# Problem Definition

## Description

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:**

```plaintext
Input: "A man, a plan, a canal: Panama"
Output: true
```

**Example 2:**

```plaintext
Input: "race a car"
Output: false
```

## Notes