CSCI 151 - Lab 10
Binary Search Trees

Overview

In this lab, we will implement a Binary Search Tree and visualize the processes of insertion, deletion, and rotation.

Materials

Setup

  1. Download the skeleton for this project.
  2. Unpack the code into a new Eclipse Java project.

Description

We can efficiently store information with Lists, but determining if an element is present could take a linear search through each element if the data is not sorted. At best, sorting will take O(n log n), and so we explore an alternative here which incorporates the idea of binary search into a linked structure of nodes.

Our items to be stored and compared in this lab will be strings. For testing purposes, I recommend using single letters as entry, however, full words can also be used.

Methods that remain to be implemented in the TreeNode class have been marked with TODO for easy identification.

Step 1: insert() and contains()

Complete the insert() and contains() methods in the TreeNode class. The test case BinarySearchTreeTester.test1() should pass if your solutions are correct.

Step 2: Tree Statistics and Visualization

Complete the height(), size(), getMin(), and getMax() methods in the TreeNode class. Then run BinaryTreeApp. As you add nodes to your tree, you should see the statistics updated on the left. Make sure the values are correct by experimenting with different tree structures.

Step 3: Traversals

Complete the preOrder(), postOrder(), and inOrder() methods in the TreeNode class. The parameter is a Consumer object that performs an operation on each value. They should pass their unit tests, and also you can test them in BinaryTreeApp.

Step 4: Deletion

Implement the remove() method. Note that it does not return the removed node; it returns the node upon which it was invoked, and rebuilds the tree as it exits from its recursive calls. Follow the comments carefully. It should pass its unit tests and again is testable on the GUI, by clicking on nodes you wish to remove.

Step 5: Rotations

Implement left and right rotations. When correct, they should pass their unit tests, and you can also test them in the GUI by clicking on the node that you wish to rotate. As with remove(), these methods return the rebuilt tree nodes.

Step 6: Evaluation

Create trees with 3, 7, and 15 nodes. First, create a balanced tree. Next, erase the tree and create a degenerate tree that is completely linear. Then, use rotations to transform each linear tree into a balanced tree. Record in your evaluation document the number of rotations you needed to perform to balance each tree. Discuss how you identified the need for a rotation when examining each tree.

What to Hand In

Submit TreeNode.java as well as your evaluation document.

Grading

20 points total:
Cumulative ProgressPoints Earned
Step 18
Step 211
Step 313
Step 415
Step 517
Step 620
© Gabriel Ferrer, Hendrix College