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Starter code
(Updated docstring for merge_alternating) [submit]
Task 1 – More Stack Exercises
In this exercise, you’ll practice using stacks. Once again, your code should only use the four methods defined in the stack public interface, and not use anything else about a stack implementation. If you try to access the _items attribute, you will likely get a 0 on this part of the exercise.

In the starter code, your first task is to implement two functions that operate on Stacks. If you get stuck, review the functions you created to work with Stacks so far! You’ll probably find some inspiration. 😉

Task 2 – A Chain of People
In this task, you’ll begin thinking about a new way to model lists, using links between nodes. We’ll start with a concrete (iron?) example.

Iron Man saves people.

Consider the situation illustrated in the picture above: some people are forming a human chain. This chain has a leader, who is holding onto someone, who is holding onto someone else, etc. Note that the last person in the chain isn’t holding onto anyone. For simplicity, we store only two pieces of information about each person: their name, and the “next” person in the chain, i.e., who they are holding onto.

We’ve provided a simple model of this situation in the starter code, consisting of two classes: PeopleChain and Person. The constructor is provided for you – try reading the code if you’d like, but this isn’t necessary for completing this task. We’ll talk about the details next week!

Implement the PeopleChain methods get_leader, get_second, get_third, and get_nth. Note that get_nth generalizes the other three methods, meaning all three of them could be implemented with get_nth. You can do this if you want, but we strongly recommend that you implement the methods in the order provided, to get a good feeling of what’s going on.

Finally, one implementation restriction is that you must implement get_nth with a for or while loop. In particular, if you know what recursion is already, don’t use it here! (You’ll use recursion to your heart’s content soon enough, my friend.)

Hint: if you need help, think about looping through the first n people in the chain. Have a variable store a reference to the “current person”; how would you advance from the current person to the next person? Take a look at the PeopleChain constructor for a bigger hint.

Do not use eval for this (or any other) exercise.