Description

Overview

In this lab, we will explore a new useful data structure: Binary Trees.  A binary tree is a very efficient data structure to store and retrieve sorted data.  They are frequently used to implement maps and dictionaries (multimaps).  In this lab, you will implement a simple form of binary trees.

Getting started

Create a new directory in your main development directory (probably on Desktop/CSE30) called Lab_11.  Try to use the terminal on your own, without getting help from the TA to setup the new directories (try to learn/remember the terminal commands).

The g++ syntax to compile classes is slightly dierent than for a single program comprised of a main (and potential functions):

g++ class1.h class1.cpp class2.h class2.cpp mainSource.cpp -o executable

where:

• g++ is the compiler (installed on your Linux system) of C++ source files,
• cpp is the source file for your main program (main function),
• h is the class declaration for your 1st class,
• cpp is your 1st class definition,
• h is the class declaration for your 2nd class,
• cpp is your 2nd class definition (and so on…),
• -o tells the compiler that you want to give the executable its own name, and  executable is the name you want to give your program.

As an example, if we have a main source file called Exercise1.cpp, the class declaration called LinkedList.h, the class definition called LinkedList.cpp, and want to create an executable called aTestProgram, you would type:

g++ LinkedList.h LinkedList.cpp Exercise1.cpp -o aTestProgram

Assuming that your program compiled successfully (i.e. no errors were found), you can run your program as you normally would by typing “./aTestProgram” in the terminal/console.

Good coding practices (worth 2 points!)

Writing code that is understandable by humans is as important as being correct for compilers.  Writing good code will help you complete the code, debug it and … get good grades.   It is very important to learn as soon as possible, because bad habits are hard to get rid of and good habits become effortless.   Someone (guess who) reads your code will be in a better mood if it is easy to understand … leading to better grades!   This lab will include 2 points (10% for code quality):

• Explanations with comments
• Meaningful names
• Indenting of blocks { }  and nesting …
• Proper use of spaces, parentheses, etc. to
• Visible, clear logic
• One / simple statements per line
• Anything that keeps your style consistent

(Exercise)

In this part of the lab, you will be implementing the basic functions for a Binary Tree, which are provided in the class declaration BTree.h (on CatCourses).  In other words, you have to create and implement the class implementation in a file called BTree.cpp.  The main file you have to use for this lab is also provided on CatCourses (Exercise.cpp).  DO NOT modify the class declaration (BTree.h) or main file (Exercise.cpp).  Looking at the class declaration, you will find that a Node is defined as a structure comprised of a key value (key_value, of type int) and two pointers to the child nodes (left and right, of type Node pointer).  You will also notice (under private) that you will be keeping track of your Binary Tree using a Node pointer, root. This root pointer should always point to the root element of your Binary Tree. If the Binary Tree is empty, the root pointer should point to NULL.

In this part of the lab, you will need to implement the following functions for the BTree class:

• Default Constructor: initializes the root, the binary tree is empty.
• Destructor: deletes the entire Binary Tree by calling destroy_tree().
• BTree_root(): returns a pointer pointing to the root of the Binary Tree.
• destroy_tree(node *leaf): a recursive function that destroys a subtree with the input argument (leaf) as root. This function will check if leaf exists, then recursively destroy its left and right child nodes.
• insert(int key, node *leaf): a recursive function that compares the input argument key with the key_value of the other input argument leaf. If key is less than key_value, the same function is called with the left child node of leaf as the new input argument; otherwise, the right child node of leaf will be used as the new input argument.  When the leaf node is empty (NULL), a new node is created and its key_value is set to key (remember to set its left and right child nodes to NULL).
• search(int key, node *leaf): a recursive function that compares the input argument key with the key_value of the other input argument leaf. It returns the pointer to leaf if key = key_value.  If key < key_value, the same function is called with the left child node of leaf as the new input argument; otherwise, the right child node of leaf will be used as the new input argument. It returns NULL if leaf is NULL (it reaches the end of the tree but the key is not found).
• insert(int key): a public function that inserts a key into the tree. It creates a new node as root with key_value equals to key if the tree is empty, otherwise it calls insert(key, root) to insert the key at the correct location.
• search(int key): a public function that starts the search of the input argument key from the root node. It returns the pointer to the node that has the same key_value as key (you do not need to perform any comparison in this function, only need to call search(int key, node *leaf) with the correct input argumentsto start the search).
• destroy_tree(): a public function that calls destroy_tree(node *leaf) with the correct input argument to destroy the whole tree.

Note:

• a pointer does not point to anything unless you 1) use the reference operator (&) in front of a variable, 2) you dynamically allocate memory for it (using the new operator), or 3) you assign it (set its value to) to another pointer
• every time you want to create a node, you will have to use the new operator
• every time you allocate memory dynamically for a pointer using the new keyword, you have to make sure that you de-allocate the memory once you do not need the data anymore. This can be done using delete (in the destructor, clear and remove functions).

Sample output from Exercise.cpp:

Root has key: 10

Left child of root has key: 6

Right child of root has key: 14

Searching for key 14…

Key 14 found!

Its left child has key: 11

Its left child has key: 18

Searching for key 13… Key 13 not found!