Short Project 6

Move items in list

In this short programming project you will be writing a function that takes a list, and index, and a direction ("left" or "right") as arguments. The goal of the function is to move the item at index to the provided direction skipping over all zeros and taking the place of another item that is not zero. If reaching the end (either left or right end) and all of the items are zero, take place of the last item.

Name the program move_item.py. Make sure that gradescope gives you the points for passing the test cases.

Examples

original_list = ["a", 0, 0, "b", "c", 0, 0]
print( move_item(original_list, 3,  "left") )

['b', 0, 0, 0, 'c', 0, 0]

original_list = ["a", 0, 0, "b", "c", 0, 0]
print( move_item(original_list, 3, "right") )

['a', 0, 0, 0, 'b', 0, 0]

# call the function again
print( move_item(original_list, 4, "right") )

['a', 0, 0, 0, 0, 0, 'b']

Development Strategy

The easiest way to implement this is using two while loops (one for going to the left, another for going to the right). You have the starting point of the item you want to move (the "index") – you need to find out where it needs to end.

Your first guess for the end index should be minus one on the index if you are going to the left or plus one on the index if you are going to the right. In your while loop you need to keep subtracting one or adding one (depending on your direction) until you reach your end destination – meaning, you skip over the zeros until you either reach the beginning of the end of the list (depending on the direction you are going) or you found an item to replace (something that is different than zero).

Before You Begin

This section gives you a quick recap of what we covered in class or introduces any new tips or examples that might help you complete the assignment. Take a few minutes to read through it before you begin.

Lists

You can access an item in a list using an index:

my_list = [0, 0, 2, 0, 0, 1]

What’s the index for value 2 and 1?

You can replace an item in a list using an index:

my_list = [0, 0, 2, 0, 0, 1]
my_list[1] = 5
my_list

[0, 5, 2, 0, 0, 1]

Lists

Here is the list:

my_list = [0, 0, 2, 0, 0, 1]

How do we move value 1 to where value 2 is, replacing 1 with zero so the list looks like this:

my_list = [0, 0, 1, 0, 0, 0]

Swapping list values

We want to go from this:

my_list = [0, 0, 2, 0, 0, 1]

To this:

my_list = [0, 0, 1, 0, 0, 0]

We do this:

index_a = 2
index_b = 5
my_list[index_a] = my_list[index_b]
my_list[index_b] = 0