1. Given a list of non-unique integers and a target value, return the count of how many pairs of integers sum to the target value 2. Write a square root function (without using a built-in or library square root function) 3. Given a sorted linked list, remove all duplicate nodes 4. Implement a class that uses entry/exit swipe information (card, swipe, station) to answer queries of average transit time between pairs of stations. (design and implement api)