Simple URL Shortener

Algorithms Data Structures System Design

Implement a simplified URL shortening service. Your solution should include the following functionalities:

  1. Shorten URL: Given a long URL, generate a short alias (e.g., a 6-character alphanumeric string) to represent it. Ensure that the same long URL always returns the same short alias.

  2. Retrieve URL: Given a short alias, return the original long URL. Handle the case where the provided alias does not exist.

  3. Update and Delete: Provide mechanisms to update an existing URL mapping and to delete a mapping.

  4. Collision Handling: Consider the possibility of short alias collisions. Ensure that your solution handles these gracefully.

  5. Edge Cases: Think about and address edge cases such as invalid URLs, repeated requests for shortening the same URL, and non-existent aliases for retrieval.

Assume the service runs on a single machine, and focus on the underlying data structures and algorithms required to implement the system efficiently. You can use any programming language of your choice.

Develop your solution in a modular manner, and include accompanying comments or documentation explaining your design decisions.