In addition to requiring you to get splay trees to work, I also want you to learn some basic things about
Java Strings, so you will build trees of Strings instead of int’s. For example, you will need to use compareTo
(or compareToIgnoreCase – we will need to discuss which) to compare two Strings.
Add whatever is necessary so that the three classes below behave correctly. Leave all variables, method
names, and code fragments exactly as they appear. Only add code to make the methods work. Do not add a
setString method in the StringNode class.
Insert is easier than search so I recommend you work on that first. You will find reference to “top-
down” algorithms when you scan the Web. Do not do that. Use the algorithm as described in class and in
the Week 5 posting. In terms of implementing backtracking it is really nothing more than what you do after
making a recursive call. With insert, for example, you will make the usual recursive calls to insert and then
after the call you will have to deal with the splay. There are two cases. (1) If the element you inserted is a
child of the current node then it is not time to splay since we always splay two levels. (2) If the element is
not a child you need to determine (a) if it’s to the left or right of the current node and (b) whether to do a zig-
zig or a zig-zag. Make appropriate calls to the rotate methods to get the job done.
You might also have to do a final zig at the root if the splaying came out odd. This is best done in the
driver program.
Search is more complicated because if the element is not found you still must splay something to the
root. You will splay the last node visited before landing on null. For example, looking at the last tree drawn
in week5-lecture.pdf, if searching for 65, 60 will be splayed to the root. If searching for 5, 10 will be splayed.
But there is an additional complication. While backtracking, how do you tell your method what is
being splayed? You passed in a value to search and if it wasn’t found you must splay a different value. This
means you need to be able to change the parameter value so that when backtracking the parameter has
changed from the value being searched for to the value being splayed. That is why WrapString is used in the
recursive search (and only there). You will then be able to use a statement like this in your recursive search
to change the value of the String being searched to the String being splayed:
str.string = t.getString();
As always, I’d love to see some questions and conversations on Discussion.
Submission and other details. Many of you did not follow rules 2 – 4 from the last assignment despite my
pleas and threats to take off points. I will be less lenient this time. Of course this time the name of your file
should be prog2.java. This should not be the name of your class. Also do not use the word package
anywhere. I spent a lot of time editing “package” out of your programs, fixing class names, and numerous
other changes. Please don’t make me do that this time. Also, as some of you are aware, if you submit
multiple times Canvas tacks a suffix onto your file name. I can live with that. Just make sure the base part of
the file name is prog2.java. Finally, though it should go without saying, the program you turn in must be
your own work. Do not copy code from someone else. Do not share your own code.
