Project 1: Virtual Directory Trees

Note: You must work independently on this assignment.

In this project, you will complete a binary search tree implementation and use the BST to store references to other directories thus representing a virtual directory tree. You will dynamically list, create, and destroy directories based on input to the program.

Goals for this project

By the time you have completed this project, you should:

  • fully understand the use and implementation of a binary search tree

  • be comfortable working with a general tree (a directory can have any number of subdirectories)

Project Preparation

This project will use almost the same files as lab5. However, you will have to make some modificiations to your bst.cpp in order to define the new functions, and alter the return values of a few functions.

To begin create a proj2 directory (assuming you haven't already done so):

mkdir -p cs24/proj2

Change into the proj2 directory and copy the files you will need for this project:

cd cs24/proj2
cp ~bboe/public_html/cs24_m13/code/proj2/* .

Then you will want to copy your bst.cpp file from your lab5 directory.

cp ../lab5/bst.cpp .

Starting the project

Open up virtual_directory.cpp and start reading the comments. They explain which functions you should start first. You should not start working on BST::remove and remove_directory until you have everything else working perfectly. However, make sure you save plenty of time as BST::remove is the most complicated piece of this assignment.

Part 2

You will need to have make_directory, list_directory and change_directory working 100% before starting part 2. Send a private piazza message to receive a copy of my part1 code.

In part two you must complete the following tasks (you should write them in this order):

  1. Implement the BinaryNode<T> *BST<T>::remove(T item) method (bst.cpp). Return NULL if item is not found in the BST, otherwise remove the Binaryode from the tree and return a pointer to the BinaryNode (do not deallocate the BinaryNode in this function). You will need to implement the BinaryNode<T> *find_max(BinaryNode<T> *node) method to help you. When it comes time to call find_max from within your recursive delete function you would call it via BST::find_max(root_of_subtree).

  2. Implement the remove_directory function (virtual_directory.cpp). The function takes in the current directory and a string containing the name of the directory to remove. The directory matching name should be removed from cwds list of children if it exists, otherwise output the error message if the directory does not exist. Make sure to deallocate any memory at this point that requires deallocation.

  3. Implement the Binarynode<T> *BST<T>::remove_root() method (bst.cpp). Remove and return the root of the tree if such a BinaryNode exists, otherwise return NULL.

  4. Implement the Directory destructor Directory::~Directory (just add this function somewhere near the top of virtual_directory.cpp). When a Directory is destructed it should clean up any allocations that are associated with that directory. That includes deallocating any of its subdirectories (use BST::remove_root as many times as necessary, which will implicitly recursively remove any of its children and so on).

  5. Implement the BST destructor BST::~BST (bst.cpp). The destructor should deallocate any memory it directly allocated, i.e., the BinaryNode instances, but it is not responsible for deallocating items that are stored within them (nor should it as you cannot assume T is a freeable type). NOTE: This function needs to deallocate memory in all cases, even if you don't end up using one of those cases directly in project 2.

Part 2 Hints

Recursive remove helper function

The recursive remove helper function can be pretty tricky to delcare correctly so the following is how I recommend you declare the function:

template <class T>
BinaryNode<T> *remove_recursive(BinaryNode<T> *node, T item,
                                BinaryNode<T> **retval) {
    // Below is an example of how you might structure this function.
    if (MATCH) {
        // Write the code for the three remove cases
        // Update retval and return the appropriate new root of the subtree
    }
    else if (GO_LEFT)
         node->set_lhs(remove_recursive<T>(node->get_lhs(), item, retval));
    else if (GO_RIGHT)
         node->set_rhs(remove_recursive<T>(node->get_rhs(), item, retval));
    else { /* Do you need this? */ }

    /* The return value should point at the updated root of the subtree.
       If the current node isn't being removed then the return should
       not be altered. If the current node is being removed *retval should
       be set to the node that has been removed from the tree (and contains
       the T that is being removed) and the return value should point to
       the new root of the subtree.
     */
    return node;
}

Note that the compiler has a hard time determining whether or not the T item is a reference. To disambiguate we need to specify the template that is used when we call the funciton. To help a bit more since I don't want you to struggle with this part, I'll provide you with the base function that you should use (should be in bst.cpp):

template <class T>
BianryNode<T> *BST<T>::remove(T item) {
    BinaryNode<T> *retval = NULL;
    root = remove_recursive<T>(root, item, &retval);
    return retval;
}

Building and testing the project

To build the project run:

make

If successful that will produce virtual_directory which you can run via:

./virtual_directory

This program has it's own set of commands which you can list via the command help. You will need to get all these commands works.

 
 

Template design by Andreas Viklund