Computer Science CS221 Test 2 Name. 1. Give a definition of the following terms, and include a brief example. a) Big Oh

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1 Computer Science CS221 Test 2 Name 1. Give a definition of the following terms, and include a brief example. a) Big Oh b) abstract class c) overriding d) implementing an interface 10/21/1999 Page 1 of 7

2 2. The goal of generic programming is to save work by writing one method to perform a task (for example, sorting) which works no matter what type of data you want to perform the task with. Unfortunately, work doesn t generally disappear completely, but tends to pop up in some other area. In generic programming as we have discussed it (i.e. writing methods that work on objects of type Comparable), where do we see this extra work? 3. Attached you will find the source code for the Comparable interface. Write a method to examine the values in an array of Comparables and move the two largest values to positions 0 and 1 in the array. The values originally in the first two positions should be switched with the value that replaces them. This is a procedure, with the array provided as a parameter. As an example, if we pass in an array of MyInteger objects with the values {9, -27, 35, 109, 7, 2, 47} the contents of the array after the method has been called should be {109, 47, 35, 9, 7, 2, -27}. use the back of the page if you need additional room. 10/21/1999 Page 2 of 7

3 4. For each of the following code fragments, give the Big Oh value for the running time and briefly explain your answer: a) int x = 0; int y = 1; x = x + y; y = x + y; b) Assume n has been read in earlier. int x = 0; for (int i = 0; i < n * 2; i++) for (int j = i; j > 0; j--) for (int k = 0; k < n * j; k++) x = (x + 1) * (-1); c) Assume that limit has been read in earlier. int x = 0; int i = 0; while (i < limit) { for (int k = 0; K < limit; k++) x = x * 2; i++; } d) Assume that n has been read in earlier. int counter = 0; for (int i = 0; i < Math.pow(n, 3); i++) for (int k = 0; k < n/2; k++) counter++; 10/21/1999 Page 3 of 7

4 5. For each of the following expressions describing the running time of a program, give the Big Oh complexity class that the algorithm falls into. Briefly explain your answer. 1 a) -----N N N b) 5NlogN + N 2 c) 5NlogN + 50N d) 5 + 3* Show the contents of the stack at each stage of the evaluation of the postfix expression * 7. Give the value of the following postfix expressions (no need to show the stack on these) a) 4 3 * / + + b) / 5 / 2 / 5 / c) /21/1999 Page 4 of 7

5 Computer Science Test 2 Fall The Stack interface is attached to the test. Write a method that takes a Stack as its parameter and modifies the stack so that it contains the contents of the original stack, but with the bottom element of the stack deleted. So, for example, if your stack originally looked like this: then your stack should look like this when the method terminates: If the original stack is empty, the method should do nothing. Note that since you are passing a reference to a Stack, changes that you make to the stack are visible outside your method. You may use another locally declared stack in your solution, but no other additional memory (i.e. no arrays or local variables). Recall that the concrete class we have used which implements the Stack interface is called StackAr. Use the back of the page if you need additional room. Pledge: On my honor, I have neither given nor received unauthorized help on this work. Signed: 10/21/1999 Page 5 of 7

6 package Supporting; * Protocol for Comparable objects. Mark Allen Weiss public interface Comparable { * Compare this object with rhs. Rhs the second Comparable. 0 if two objects are equal; * less than zero if this object is smaller; * greater than zero if this object is larger. int compares( Comparable rhs ); } * Compare this object with rhs. Rhs the second Comparable. true if this object is smaller; * false otherwise. boolean lessthan( Comparable rhs ); 10/21/1999 Page 6 of 7

7 package DataStructures; import Exceptions.*; // Stack interface // ******************PUBLIC OPERATIONS********************* // void push( x ) --> Insert x // void pop( ) --> Remove most recently inserted item // Object top( ) --> Return most recently inserted item // Object topandpop( ) --> Return and remove most recent item // boolean isempty( ) --> Return true if empty; else false // void makeempty( ) --> Remove all items // ******************ERRORS******************************** // top, pop, or topandpop on empty stack * Protocol for stacks. Mark Allen Weiss public interface Stack { * Test if the stack is logically empty. true if empty, false otherwise. boolean isempty( ); * Get the most recently inserted item in the stack. * Does not alter the stack. the most recently inserted item in the stack. Underflow if the stack is empty. Object top( ) throws Underflow; * Remove the most recently inserted item from the stack. Underflow if the stack is empty. void pop( ) throws Underflow; * Return and remove the most recently inserted item * from the stack. the most recently inserted item in the stack. Underflow if the stack is empty. Object topandpop( ) throws Underflow; * Insert a new item into the stack. x the item to insert. void push( Object x ); } * Make the stack logically empty. void makeempty( ); 10/21/1999 Page 7 of 7