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CSE143 Midterm
Spring 2012
Name of Student_______________________________________________________________
Section (e.g., AA)___________________ TA_____________________________________
The exam is divided into six questions with the following points:
# Problem Area Points Score
---------------------------------------------
1 Recursive Tracing 15 _____
2 Recursive Programming 15 _____
3 Linked Lists 15 _____
4 Details of Inheritance 20 _____
5 Stacks/Queues 25 _____
6 Array Programming 10 _____
----------------------------
Total 100 _____
This is a closed-book/closed-note exam. Space is provided for your answers.
There is a "cheat sheet" at the end that you can use as scratch paper or to
write answers. You are not allowed to access any other paper during the exam
(not even scratch paper). Use the backs of the pages of this test if
necessary. Anyone caught with extra paper will lose at least 10 points.
The exam is not, in general, graded on style and you do not need to include
comments. For the stack/queue question, however, you are expected to use
generics properly and to declare variables using interfaces when possible.
The cheat sheet mentions important restrictions on Stacks and Queues that you
must follow.
You are allowed to abbreviate "compiler error" and "runtime error" for the
inheritance question (as in "ce" and "re" or "c.e." and "r.e."), but you should
otherwise NOT use any abbreviations on the exam.
You are NOT to use any electronic devices while taking the test, including
calculators. Anyone caught using an electronic device will receive a 10 point
penalty.
Do not begin work on this exam until instructed to do so. Any student who
starts early or who continues to work after time is called will receive a 10
point penalty.
If you finish the exam early, please hand your exam to the instructor and exit
quietly through the front door.
1. Recursive Tracing, 15 points. Consider the following method:
public void mystery(int n) {
if (n == 1) {
System.out.print(n);
} else {
System.out.print(n + ", ");
if (n % 2 == 0) {
mystery(n / 2);
} else {
mystery(3 * n + 1);
}
}
}
For each call below, indicate what output is produced:
Method Call Output Produced
mystery(1); ___________________________________________
mystery(2); ____________________________________________
mystery(4); ____________________________________________
mystery(8); ____________________________________________
mystery(10); ____________________________________________
2. Recursive Programming, 15 points. Write a recursive method called
printDashed that takes an integer as a parameter and that prints the integer
with dashes in between the digits.
The table below shows sample calls and the output that should be produced:
Method call Output Method call Output
------------------------------ ---------------------------------
printDashed(-834) -8-3-4 printDashed(6) 6
printDashed(-17) -1-7 printDashed(42) 4-2
printDashed(-4) -4 printDashed(983) 9-8-3
printDashed(0) 0 printDashed(29348) 2-9-3-4-8
Notice that no dashes are printed for positive one-digit numbers and that a
leading dash is printed only for negative numbers. You are not allowed to
construct any structured objects (no array, ArrayList, String,
StringBuilder, etc) and you may not use a while loop, for loop, or do/while
loop to solve this problem; you must use recursion.
3. Linked Lists, 15 points. Write a method called removeLast that removes and
returns the last value of a list of integers. For example, if a variable
called list stores the following values:
[3, 6, 19, 24, -8, 0, 14]
and you make the following call:
int n = list.removeLast();
the variable n will be set to 14 and list will store:
[3, 6, 19, 24, -8, 0]
Your method should throw a NoSuchElementException if the list is empty.
You are writing a method for the LinkedIntList class discussed in lecture:
public class ListNode {
public int data; // data stored in this node
public ListNode next; // link to next node in the list
<constructors>
}
public class LinkedIntList {
private ListNode front;
<methods>
}
You may not call any other methods of the LinkedIntList class and you may
not construct any structured objects to solve this problem.
4. Details of inheritance, 20 points. Assuming that the following classes have
been defined:
public class Gorge extends Cliff {
public void method2() {
System.out.println("Gorge 2");
}
public void method3() {
System.out.println("Gorge 3");
}
}
public class Hill extends Peak {
public void method2() {
System.out.println("Hill 2");
}
public void method3() {
System.out.println("Hill 3");
}
}
public class Peak {
public void method1() {
System.out.println("Peak 1");
method3();
}
public void method3() {
System.out.println("Peak 3");
}
}
public class Cliff extends Peak {
public void method3() {
System.out.println("Cliff 3");
super.method3();
}
}
And assuming the following variables have been defined:
Peak var1 = new Cliff();
Gorge var2 = new Gorge();
Peak var3 = new Hill();
Peak var4 = new Gorge();
Peak var5 = new Peak();
Object var6 = new Cliff();
In the table below, indicate in the right-hand column the output produced by
the statement in the left-hand column. If the statement produces more than one
line of output, indicate the line breaks with slashes as in "a/b/c" to indicate
three lines of output with "a" followed by "b" followed by "c". If the
statement causes an error, fill in the right-hand column with either the phrase
"compiler error" or "runtime error" to indicate when the error would be
detected.
Statement Output
------------------------------------------------------------
var1.method1(); ____________________________
var2.method1(); ____________________________
var3.method1(); ____________________________
var4.method1(); ____________________________
var5.method1(); ____________________________
var6.method1(); ____________________________
var1.method2(); ____________________________
var2.method2(); ____________________________
var3.method2(); ____________________________
var1.method3(); ____________________________
var2.method3(); ____________________________
var3.method3(); ____________________________
((Gorge)var6).method1(); ____________________________
((Cliff)var3).method2(); ____________________________
((Gorge)var4).method2(); ____________________________
((Gorge)var3).method2(); ____________________________
((Hill)var3).method2(); ____________________________
((Gorge)var1).method1(); ____________________________
((Cliff)var4).method3(); ____________________________
((Peak)var6).method3(); ____________________________
5. Stacks/Queues, 25 points. Write a method called removeMin that takes a
stack of integers as a parameter and that removes and returns the smallest
value from the stack. For example, if a variable called s stores the
following sequence of values:
bottom [2, 8, 3, 19, 7, 3, 2, 42, 9, 3, 2, 7, 12, -8, 4] top
and you make the following call:
int n = removeMin(s);
the method removes and returns the value -8 from the stack, so that the
variable n will be -8 after the call and s will store the following values:
bottom [2, 8, 3, 19, 7, 3, 2, 42, 9, 3, 2, 7, 12, 4] top
If the minimum value appears more than once, all occurrences of the minimum
should be removed from the stack. For example, given the ending value of
the stack above, if we again call removeMin(s), the method would return 2
and would leave the stack in the following state:
bottom [8, 3, 19, 7, 3, 42, 9, 3, 7, 12, 4] top
You are to use one queue as auxiliary storage to solve this problem. You
may not use any other auxiliary data structures to solve this problem,
although you can have as many simple variables as you like. You also may
not solve the problem recursively. Your solution must run in O(n) time
where n is the size of the stack. Use the Stack and Queue structures
described in the cheat sheet and obey the restrictions described there.
6. Array Programming, 10 points. Write a method called mirror that doubles the
size of a list of integers by appending the mirror image of the original
sequence to the end of the list. The mirror image is the same sequence of
values in reverse order. For example, if a variable called list stores this
sequence of values:
[1, 3, 2, 7]
and you make the following call:
list.mirror();
then it should store the following values after the call:
[1, 3, 2, 7, 7, 2, 3, 1]
Notice that it has been doubled in size by having the original sequence
appearing in reverse order at the end of the list.
You are writing a method for the ArrayIntList class discussed in lecture:
public class ArrayIntList {
private int[] elementData; // list of integers
private int size; // current # of elements in the list
<methods>
}
You are not to call any other ArrayIntList methods to solve this problem,
you are not allowed to define any auxiliary data structures (no array,
ArrayList, etc). You may assume that the array has sufficient capacity to
store the new values.
CSE143 Midterm Cheat Sheet
Queues should be constructed using the Queue<E> interface and the
LinkedList<E> implementation. For example, to construct a queue of String
values, you would say:
Queue<String> q = new LinkedList<String>();
Stacks should be constructed using the Stack<E> class (there is no interface).
For example, to construct a stack of String values, you would say:
Stack<String> s = new Stack<String>();
To transfer from a queue to a stack:
while (!q.isEmpty())
s.push(q.remove());
To transfer from a stack to a queue:
while (!s.isEmpty())
q.add(s.pop());
-------------------------------------------------------------------------------
For Stack<E>, you are limited to the following operations:
public void push(E value); // push given value onto top of the stack
public E pop(); // removes and returns the top of the stack
public boolean isEmpty(); // returns whether or not stack is empty
public int size(); // returns number of elements in the stack
For Queue<E> you are allowed the following operations:
public void add(E value); // inserts given value at the end of the queue
public E remove(); // removes and returns the front of the queue
public boolean isEmpty(); // returns whether or not queue is empty
public int size(); // returns number of elements in the queue
YOU ARE NOT ALLOWED TO USE FOREACH LOOPS OR ITERATORS FOR EITHER STRUCTURE.
-------------------------------------------------------------------------------
Below is an example of a method that could be added to the LinkedIntList class
to compute the sum of the list:
public int sum() {
int sum = 0;
ListNode current = front;
while (current != null) {
sum += current.data;
current = current.next;
}
return sum;
}
]]>
Stuart Reges
Last modified: Fri Sep 16 16:16:07 PDT 2011