CS307 fall 2006, Midterm 1 Key and Grading Criteria:

Grading acronyms

OBOE - Off by one error. Calculation is off by one.
AIOBE - Array Index out of Bounds Exception will occur
NPE - Null Pointer Exception will occurs
ABA - Answer by Accident
GCE - Gross Conceptual Error. Did not answer the question asked or showed fundamental misunderstanding
NAP - No answer provided. No answer given on test
ECF - Error carried forward. 
BOD - Benefit of the Doubt. Not certain code works, but, can't prove otherwise
Gacky - Code very hard to understand even though it works

Question 1. Same as key or -2. Ignore differences in spacing, capitalization.

A. 4 11

B. 16 14

C. 19

D. 4 6 7

E 9 2 3

F. Yes. The comment does nothing to enforce the precondition so someone could
still send null as a parameter. (Or words to that effect. Note, the test
instructions stated to assume preconditions were true on methods that the
student writes. The student is not writing this method.)

G. false

H. 15

I 10

J. Thrown out. All students get credit. Question had unintended
recursion. I intended to call super.cost, but did not.

K. Syntax Error

L. 2040 (20 40 okay too.)

M. No, the class will not compile because it did not implement all of the
methods from the interface, (Or words to that effect.)

N. Yes, it inherits the Object class version of toString.

O. Yes. Could have called the baseCost method instead of referencing the
basePlanCost instance variable. (Or words to that effect.)


Question 2 (Suggested Solution.)

public static void fixData(int[] data){
	int lastGoodIndex;
	int currentIndex = 0;
	while(currentIndex < data.length){
		if( data[currentIndex] == -1){
			//we have found the start of bad data
			lastGoodIndex = currentIndex - 1;

			// go find the index of the next good element of data
			while(data[currentIndex] == -1)
				currentIndex++;
			int diff = (data[currentIndex] - data[lastGoodIndex]) 
				/ (currentIndex - lastGoodIndex);

			//correct the bad data
			for(int i = lastGoodIndex + 1; i < currentIndex; i++){
				data[i] = data[i - 1] + diff;
			}
		}
		else
			// current data is good. go on to next element
			currentIndex++;
	}
}

Break down of points:
Loop through array 2 points
Identify start of bad data
	attempt 2 points
	correct 2 points
Count number of elements in bad section
	attempt 3 points
	correct 5 points
calculate interpolated increase per element
	attempt 3 points
	correct 5 points
add increment to elements in bad section
	attempt 3 points
	correct 5 points


Question 3.

suggested solution:
public int[] numElementsEqualToTarget(int[][] mat, int target){
	int[] result = new int[ mat[0].length ];
	for(int r = 0; r < mat.length; r++)
		for(int c = 0 C < mat[0].length; c++)
			if( mat[r][c] == target )
				result[c]++;
	
	return result;
}

correctly declaring result. Size must be correct. 2 points
looping through rows 4 points
looping through columns 4 points
checking to see if element is match 4 points
correctly updating result for match 4 points
returning result 2 points

Some confusion on rows vs. columns


Question 4.

suggested solution:

public class Apartment{
	private int myBedrooms;
	private int myRent;
	private int mySqFt;
	private double myBathrooms;

	public Apartment(int bedrooms, int rent, int sqFt, int bathrooms){
		myBedrooms = bedrooms;
		myRent = rent;
		mySqFt = sqFt;
		myBathrooms = bathrooms;
	}

	public double avePerSqFt(){
		return 12.0 * myRent / mySqFt;
	}

	public boolean hasMoreRooms(Apartment other){
		return (myBedrooms + myBathrooms) 
			> (other.myBedrooms + other. myBathrooms);
	}
}

point break down

class header -> 1 point
instance variables -> 4 points
constructor -> 5 points
average price per square foot method -> 5 points
has more rooms method -> 5 points

possible point losses

instance vars:
instance vars not private -1
wrong type on ints -1
wrong type on double -1
missing instance var -1

constructor:
incorrect header -1
parameters missing or wrong -2
assignments -2

average price per square foot method
any parameters -1
incorrect header (name can vary) -1
int division instead of double division -1
other problems with calculation -1
missing return -1

has more rooms method
static method -1
two Apartment parameters -1
incorrect logic or calculation -1
return (myBedrooms > other.myBedrooms) && myBathrooms > other.myBathrooms); is
okay
incorrect header -1
no return -1