1. Given the head of a linked list, determine if the linked list has a cycle in it. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Return true if there is a cycle in the linked list. Otherwise, return false.
2. Share your experience writing user guides.
3. Create a basic React app with dummy data fetched from a JSON API.
4. Concatenate two LinkedLists without using extra space and in O(n) time.