Computer Science Code Challenges & Tips

1. Write a function that takes a string and returns the longest substring without repeating characters.

2. Implement a function to check if a given binary tree is a valid binary search tree.

3. Create a function that merges two sorted linked lists into one sorted linked list.

4. Write a function to find the k-th largest element in an unsorted array.

5. Given a string s, implement a function that determines if it is a palindrome, considering only alphanumeric characters and ignoring cases.

6. Write a function to count the number of distinct subsequences of a given string.

7. Implement a function that finds the maximum product of two integers in an array.

8. Given a matrix, write a function that rotates the matrix by 90 degrees clockwise.

9. Create a function to perform a deep copy of a linked list where each node contains a random pointer as well.

10. Write a function to find all unique triplets in an array that add up to zero.