Artificial intelligence Code Challenges & Tips

1. Implement a function that takes a list of integers and returns the two numbers that add up to a target sum. If no such numbers exist, return `None`.

2. Write a function to implement a simple linear regression algorithm from scratch, using only Python’s basic data types.

3. Create a binary tree class and implement a method to perform a level-order traversal of the tree.

4. Write a function to categorize a list of emails into valid and invalid formats based on common email validation rules.

5. Given a sequence of integers, implement a function that returns the longest increasing subsequence.

6. Implement a K-means clustering algorithm from scratch.

7. Create a maze solver that uses Depth-First Search (DFS) or Breadth-First Search (BFS) to find the shortest path through a given maze representation.

8. Write a function that generates the first `n` Fibonacci numbers using a recursive method and memoization.

9. Implement a function that takes a list of strings and returns a dictionary with each unique word as the key and its frequency in the list as the value.

10. Write a function that detects cycles in a directed graph given an adjacency list.