1. Leetcode question: trapping rainwater. 2. Design / OOP: Design classes / data structures for a restaurant that has multiple pizza types and a salad, each has dressings with some specific price and quantity. We want to be able to calculate the price of some menu item. 3. General coding problem: You have a list of 10k product items, and want to display the user 10 of those every day they log in. How can we randomly chose 10 items with equal probability at each day from the list. Write a function for that (requires you to also come up with data structure or requirements like whether the input is modified etc.)