Download CS 61B Midterm Exam I at University of California, Berkeley - Computer Science and more Exams Data Structures and Algorithms in PDF only on Docsity!
University of California at Berkeley Department of Electrical Engineering and Computer Sciences Computer Science Division
Spring 2009 Jonathan Shewchuk
CS 61B: Midterm Exam I
This is an open book, open notes exam. Electronic devices are forbidden on your person, including cell phones, iPods, headphones, and PDAs. Turn your cell phone off and leave all electronics, except your laptop, with the instructor, or risk getting a zero on the exam. Do not open your exam until you are told to do so!
Name:
Login:
Lab TA:
Lab day and time:
Do not write in these boxes. Problem # Possible Score
- Quickies 7
- Inheritance 8
- Remove node from list 10
Total 25
Problem 1. (7 points) Quickies.
a. (1 point) Briefly explain the difference between an instance variable and a class variable.
b. (1 point) Can you use the super keyword in a static method? Explain.
c. (3 points) What is the output of this program?. Explain why..
public class What { public long n;
public void increment() { n++; }
public static void reset(What w) { w.increment(); w = new What(); w.n = 0; }
public static void main(String[] args) { What w = new What(); w.n = 7; reset(w); System.out.println("The number is " + w.n); } }
d. (2 points) What’s wrong with the following code? Specifically, what does this code do? (Yes, it does compile and run.)
public class Soda { public String name;
public Soda() { Soda pop = new Soda(); pop.name = "Dr. Pepper"; }
public static void main(String[] args) { System.out.println((new Soda()).name); } }
Problem 3. (10 points) Removing a Node from a List.
a. (6 points) Write a method called removeNode in the SList class below, which implements a singly-linked list. removeNode takes an SListNode node which you know is in this list, and removes it. (Your method does not need to work, and may even crash, if node is not in the list or is null.) After you’re done, all the other nodes (that you didn’t remove) must still be in the list, in the same order as before. Your solution should manipulate next pointers directly. If you call any other methods, you must include them here. There is no size field. Your method should be fast.
public class SList { | public class SListNode { public SListNode head; | public Object item; | public SListNode next; public void removeNode(SListNode node) { | }
} Check here if your answer |---| } is continued on the back. |___|
Part b. is on the next page...
b. (4 points) Now, write the same method for a doubly-linked list in the DList class below, which is a subclass of SList. Observe that DListNode is a subclass of SListNode too. This doubly-linked list class has no sentinel; it has both a head and a tail pointer. Although the removeNode method takes an SListNode parameter (so that overriding will work correctly), you should assume that the object passed in is always a DListNode. To help you out, we’ve included a cast to give you a more useful parameter dnode. (Again, your method does not need to work, and may even crash, if node is not in the list, is null, or is not a DListNode.) Your doubly-linked removeNode method must reuse code by calling the superclass method. That way, you will only need to write code to update the tail reference or some node’s prev reference.
public class DListNode extends SListNode // inherits Object item and SListNode next public DListNode prev; }
public class DList extends SList { // inherits SListNode head public DListNode tail;
public void removeNode(SListNode node) { DListNode dnode = (DListNode) node; // Assume this cast always succeeds.
} Check here if your answer |---| } is continued on the back. |___|
Don’t forget that next and node have static type SListNode, and therefore must be cast to DListNode if you want to use their prev fields.
