Class 47: Lab: Traversing and Iterating Trees

Held Wednesday, April 26, 2000

Overview

Today we will explore techinques used to print trees and convert trees to lists.

Notes

• Warning! Not all today's code is guaranteed to be correct.
• Please send me your stub classes and interfaces (if you have not done so already).
• Please use interfaces whenever possible.
• Expect the exam on Friday.
• Don't forget to relay pizza prefs to Matt

Contents

• Required Files
• Traversing Trees
• Getting Started
• Printing
• Modifying printdfs
• Modifying printbfs
• Printing Edges in Outlines
• Adding a Size and a Depth

Summary

• Generalizing the puzzle solution: How d you iterate, visit, or list the elements of a tree?
• Preorder vs. postorder
• Depth-first vs. breadth-first
• Special Lab: Travering trees

Required Files

Interfaces:

• Tree.java
• TreeVertex.java

Implementations:

• TreeNode.java
• NodeBasedTree.java

Utilities:

• TreePrinter.java
• DoublyLinkedNode.java
• QuickQueue.java

Traversing Trees

• Suppose we want to print out the elements of a tree (or convert them to a list).
• There are three ``metrics'' involved:
  • Do we print depth-first or breadth-first?
  • Do we print a node before (prefix), after (postfix), or between (infix) its children?
  • Do we print the children in left-to-right or right-to-left order?

Getting Started

• Make copies of the files.
• Compile them. Instead of just twiddling your thumbs, move on to the following steps.
• Scan the two interfaces.
  • How is the design of these trees similar to what we discussed in class?
  • How is it different?
  • Any other surprises?
• How might you build the following tree?

      A
     / \
    B   C
   / \
  D   E
      |
      F
  

• What do you expect to happen when you delete D? When you delete B?
  • And how would you delete them?
• Scan the implementations.
  • What additional methods to you see?
  • Why do you think those methods are necessary?

Printing

• Read through TreePrinter.
  • What is the difference between the three public methods?
• For the tree given in the previous section ...
  • What do you expect printOutline to print?
  • What do you expect printdfs to print?
  • What do you expect printbfs to print?
• Confirm your answers through experimentation.

Modifying printdfs

• Write a new variant of printdfs that prints in postfix. That is, a node should be printed after its children.
• Write a newe variant of printdfs that prints its children in right-to-left order.

Modifying printbfs

• Write a newe variant of printbfs that prints its children in right-to-left order.

Printing Edges in Outlines

Using printOutline as a guide, write a method, printWithEdges that includes the edges in the outline. For example, instead of

A
  B
    Q
  E
    T
      X
      Y
      Z
    S

A
+-B
| +-Q
|
+-E
  +-T
  | +-X
  | |
  | +-Y
  | |
  | +-Z
  |
  +-S

Adding a Size and a Depth

Update the interfaces and the implementations to support getSize and getDepth methods. That is, each tree should be able to report on the number of elements it contains and the number of levels it contains.