Ruby Code Challenges & Tips

1. Write a method to find the longest substring without repeating characters in a given string.

2. Implement a function that takes an array of integers and returns the two numbers such that they add up to a specific target.

3. Create a method that merges two sorted arrays into one sorted array.

4. Write a Ruby function to count the number of occurrences of each character in a string.

5. Implement a function to determine if a given string is a palindrome, considering only alphanumeric characters and ignoring case sensitivity.

6. Write a method that takes an integer `n` and returns the first `n` Fibonacci numbers as an array.

7. Create a class that implements a basic stack with push, pop, and peek methods.

8. Write a program to sort a given array of strings in ascending order by the length of the strings, using Ruby's built-in methods.

9. Implement a method to find the intersection of two arrays, returning a new array containing only the elements present in both arrays.

10. Write a function that takes a binary tree and returns an array of its values in level-order traversal.