Homework 10

Due at 11:59:59 pm on Tuesday, 11/26/2019.

Instructions

Download hw10.zip. Inside the archive, you will find starter files for the questions in this homework, along with a copy of the OK autograder.

Submission: When you are done, submit with python3 ok --submit. You may submit more than once before the deadline; only the final submission will be scored. Check that you have successfully submitted your code on okpy.org. See this article for more instructions on okpy and submitting assignments.

Readings: This homework relies on following references:

More Practice with Trees!

Question 1: Leaves

Write a function leaves that returns a list of all the entries of the leaf nodes of a Tree.

def leaves(t):
    """Returns a list of all the entries of the leaf nodes of the Tree t.

    >>> leaves(Tree(1))
    [1]
    >>> leaves(Tree(1, [Tree(2, [Tree(3)]), Tree(4)]))
    [3, 4]
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q leaves

Question 2: Square Tree

Write a function square_tree that mutates a Tree with numerical entries so that each entry is squared.

def square_tree(t):
    """Mutates a Tree t by squaring all its elements.

    >>> t = Tree(1, [Tree(3, [Tree(5)]), Tree(7)])
    >>> square_tree(t)
    >>> t
    Tree(1, [Tree(9, [Tree(25)]), Tree(49)])
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q square_tree

More Practice with Linked Lists!

Question 3: Deep Map

Implement deep_map, which takes a function f and a link. It returns a new linked list with the same structure as link, but with f applied to any element within link or any Link instance contained in link.

The deep_map function should recursively apply fn to each of that Link's elements rather than to that Link itself.

Hint: You may find the built-in isinstance function useful.

def deep_map(f, link):
    """Return a Link with the same structure as link but with fn mapped over
    its elements. If an element is an instance of a linked list, recursively
    apply f inside that linked list as well.

    >>> s = Link(1, Link(Link(2, Link(3)), Link(4)))
    >>> print_link(deep_map(lambda x: x * x, s))
    <1 <4 9> 16>
    >>> print_link(s) # unchanged
    <1 <2 3> 4>
    >>> print_link(deep_map(lambda x: 2 * x, Link(s, Link(Link(Link(5))))))
    <<2 <4 6> 8> <<10>>>
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q deep_map

Question 4: Reverse

Implement reverse, which takes a linked list link and returns a linked list containing the elements of link in reverse order. The original link should be unchanged.

def reverse(link):
    """Returns a Link that is the reverse of the original.

    >>> print_link(reverse(Link(1)))
    <1>
    >>> link = Link(1, Link(2, Link(3)))
    >>> new = reverse(link)
    >>> print_link(new)
    <3 2 1>
    >>> print_link(link)
    <1 2 3>
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q reverse