PHP Code Challenges & Tips

1. Write a function in PHP that takes a string and returns the first non-repeating character.

2. Create a PHP function that checks if a given string is a palindrome.

3. Write a PHP script to implement a simple in-memory cache with get, set, and delete methods.

4. Develop a PHP function that accepts an array of integers and returns the two numbers that sum up to a specific target.

5. Write a PHP function to sort an array of integers using the quicksort algorithm.

6. Implement a PHP class to represent a basic binary tree, including methods for insertion and traversal (in-order, pre-order, post-order).

7. Create a PHP function that takes an array of integers and returns an array of the same integers but sorted without using any built-in sorting functions.

8. Write a function in PHP that generates all possible combinations of a given set of characters.

9. Develop a PHP script that reads a CSV file and converts it into an associative array with the first column as keys.

10. Write a PHP method to find the longest common prefix string amongst an array of strings.