1. **Easy Question:** Describe the process to find the middle element of a linked list. In your explanation, include an efficient strategy that does not require knowing the total length of the list beforehand. 2. **Easy Question:** Explain how to reverse a string in Python without using any built-in functions or slicing. Your solution should detail a method that iterates through the string and constructs the reversed version character by character. 3. **Medium Question:** Discuss the implementation of a queue using two stacks. Your explanation should cover the logic behind using two stacks to simulate the FIFO (First In, First Out) behavior of a queue, including how to optimize for either enqueue or dequeue operations. 4. **Hard Question:** Elaborate on designing a data structure that supports the following operations: insert, delete, and get_random_element, all in constant time complexity. Your solution should detail the data structures you would use, how you would maintain them to achieve constant time for each operation, and how to handle potential issues like maintaining randomness when elements are deleted.