Program #3 Solution


Categories: , Tag:


Programs must be written in C++ and are to be submitted using handin on the CSIF by the due date (see Canvas) using the command:

handin cs60 Program1 file1 file2 … fileN

Your programs must compile and run on the CSIF. Use handin to submit all files that are required to compile (even if they come from the prompt). Pro-grams that do not compile with make on the CSIF will lose points and possibly get a 0. Programs that have warnings during compilation will lose 10 out of 100 points.

An autograder along with examples and solutions will be available shortly.

  • Overview & Learning Objectives

In this program you will implement an AVL tree. There are multiple objectives of this assignment:

  1. strengthen your knowledge of JSON,

  1. strengthen your understanding of code testing,

  1. understand and implement an AVL Tree.

  • AVL Trees

Create a source file AVL.cpp and a header file AVL.h and implement an AVL Tree as a C++ class called AVLTree. A binary search tree is implemented in BST.cpp and BST.h using C++11 smart pointers weak_ptr and shared_ptr, which are built to help you manage memory. For a tutorial on smart pointers, see: Briefly, abide by the following rules to use smart pointers for your AVL tree:

If v is a parent of u, then u has a std::weak_ptr that points to v.


If w is a child of u, then u has a std::shared_ptr that points to w.

Use std::shared_ptr to modify what is being pointed to. In order to do this for a parent, you must convert a std::weak_ptr to a std::shared_ptr using lock.

To check for an empty smart pointer, compare a std::shared_ptr to nullptr.

A std::weak_ptr may not be assigned nullptr; instead, use reset to have a std::weak_ptr “point to null”.

Implement the following.

Insert Implement an Insert function that utilizes the rotations as described

at GeeksForGeeks:

Deletion Implement a Delete function as described at GeeksForGeeks: Note that the article links to BST deletion: When a node is deleted in a BST, if it has two children, either the inorder successor or the inorder predecessor is copied. Either choice is fine for this programming assignment.

DeleteMin Implement a DeleteMin function which deletes the minimum key in the AVL tree. Any implementation that runs in O(log n) time is ac-ceptable.

As usual, input will be in the form of a JSON file, and output should be printed to the screen. You can use CreateData.exe to generate input. Calling ./CreateData.exe 5 on the command line results in a file like this:


“1”: {

“key”: 2109242329,

“operation”: “Insert”


“2”: {

“key”: -948648564,

“operation”: “Insert”


“3”: {

“key”: -948648564,

“operation”: “Delete”


“4”: {

“operation”: “DeleteMin”



“5”: {

“key”: -289891961,

“operation”: “Insert”


“metadata”: {

“numOps”: 5



Which results in a tree with one node with key -289891961. Your program will read in input file such as the above, perform the operations in order, and print a JSON object to the screen (stdout) with the following format:

A height key (JSON key) whose value is the tree’s height,

A root key (JSON key) whose value is the root’s key (AVL tree key), A size key whose value is the number of nodes in the tree, and

For each node, a key/value pair where the JSON key is the node’s key and the fields are:

height the height of the node,

balance factor the balance factor of the node, (use the right-left formula for this)

parent the key of the parent node, if it exists left the key of the left child node, if it exists right the key of the right child node, if it exists

root the value of true, if the node is the root, otherwise do not include this key.

For example, the tree given by:


1 5


Is encoded by the JSON object:



“1”: {

“balance factor”: 0,

“height”: 0,

“parent”: 3


“100”: {

“balance factor”: 0,

“height”: 0,

“parent”: 5


“3”: {

“balance factor”: 1,

“height”: 2,

“left”: 1,

“right”: 5,

“root”: true,


“5”: {

“balance factor”: 1,

“height”: 1,

“parent”: 3,

“right”: 100


“height”: 2,

“root”: 3,

“size”: 4


  • AVLCommands

Write a C++ program AVLCommands.cxx that does the following:

  1. takes an input JSON filename representing a sequence of AVL tree oper-ations (Insert, Delete, and DeleteMin) as its first command-line argu-ment,

  1. creates an AVL tree using the operations described in the input JSON file,

  1. prints the resulting AVL tree JSON object to the screen (stdout).

Name your executable AVLCommands.exe and add lines to your Makefile to compile AVL.o and AVLCommands.exe.


  • Compilation

A Makefile has been provided for you. When you add new files to your program, you will need to edit this Makefile.

  • Testing your code

In addition to the autograder, you may do the following to test your code. Modify BSTSanityCheck.cxx for use with your AVL tree. The code does the following:

lines 29-39: Creates a sequence of operations to test, including Inserts, Deletes, and DeleteMins.

lines 40-44: Removes elements in sorted order from the tree, then compares the result to a sorted array.

In addition, you should incorporate the following facts:

  1. The balance factor of every node should be between -1, 0, and 1.

  1. The height of every node should be 0 for leaves, 1 + child height if a node has a single child, and 1 + the minimum of the children’s height if a node has two children.

  1. It turns out that for a tree of n nodes, an AVL tree has height less than 2 log n.

  • Files to turn in

    1. AVL.cpp

    1. AVL.h

    1. AVLCommands.cxx

    1. Makefile

    1. BST.cpp (even if you have not modified it)

    1. BST.h (even if you have not modified it)

    1. CreateData.cxx (even if you have not modified it)