CompSci 6 Spring 2006 Test 2 Solutions

Problem 1 Part A
a.  5 6 24 9 8 28

b. When an item is removed from the array, the elements shift down, but
the counter k is moved forward by one. Each time an item is removed from
the array the adjacent item one higher is shifted to its spot and not
considered.

Problem 1 Part B

The elements in "values"  from positions 0 to k-1 have been copied into 
the array temp if they are even.

Problem 2 Part A

int NumberOccurrences(String item, ArrayList<TreeSet> sets)
{
   int count = 0;
   for (TreeSet<String> current: sets)
   {
      if (current.contains(item))
         count++;
   }
   return count;
}

OR

int NumberOccurrences(String item, ArrayList<TreeSet> sets)
{
   int count = 0;
   for (int k=0; k < sets.size(); k++)
   {
      if (sets.get(i).contains(item))
         count++;
   }
   return count;
}

Problem 2 Part B

   public ArrayList<String> inTooManyClubs(ArrayList<TreeSet> membersets)
   { 
      ArrayList<String> nameList = new ArrayList<String>();
      TreeSet<String> nameSet = new TreeSet<String>(); 
      
      for (int k=0; k<membersets.size(); k++)
      {
         TreeSet<String> current = membersets.get(k);
         
         for (String name : current)
         {
            if (NumberOccurrences(name, membersets) > 3)
            {
               nameSet.add(name);
            }
         }
      }
      for (String name : nameSet)
      {
         nameList.add(name);
      }
      return nameList;
   }


Problem 3

public class BarsOn extends Command {
 
   public BarsOn ()
    {
        super("BarsOn");
    }

    public void execute (Pixmap target)
    {
        Dimension bounds = target.getSize();
        for (int x = 0; x < bounds.width - 10; x = x + 40 )
        {
            for (int y = 0; y < bounds.height; y++ )
            {
               for (int k = 0; k<10 && x+k<bounds.width; k++)
               {
                  Color black = new Color(0,0,0);
                    target.setColor(x+k, y, black);
               }
            }
        }
    }
}

OR

    public void execute (Pixmap target)
    {
        Dimension bounds = target.getSize();
        for (int x = 0; x < bounds.width; x++)
        {
            for (int y = 0; y < bounds.height; y++ )
            {
               if (x % 40 < 10)
               {
                  Color black = new Color(0,0,0);
                    target.setColor(x, y, black);
               }
            }
        }
    }










Problem 4 Part A
1. It is an abstract method. Any class that extends this class will be
forced to implement it.

2. Output is:
Answer is incorrect
The correct answer is (correct answer shown here)

3. Since Quiz is abstract, one cannot construct a Quiz object.
You cannot say "new Quiz()". Instead you would need to construct
an object that is inherited.







Problem 4 Part B

public class MathQuiz extends Quiz
{
   public MathQuiz()
   {
      super();
   }
   
   public void createQuestion()
   {
      int firstnum = myGenerator.nextInt(100);
      int secondnum = myGenerator.nextInt(100);

       int type = myGenerator.nextInt(2);
       if (type==0)  // question is add
       {
          setQuestion(firstnum + " + " + secondnum + " = ");
          setCorrectAnswer((firstnum + secondnum) + "");
       }
       else // type == 1
       {
          setQuestion(firstnum + " * " + secondnum + " = ");
          setCorrectAnswer((firstnum * secondnum) + "");
 
       }
    }
}

Problem 4 Part C.1

public HistoryQuiz(String filename)
{
   myQuestions = new ArrayList<String>();
   myAnswers = new ArrayList<String>();
   try
   {
      File data = new File(filename);
      Scanner input = new Scanner(data);
      while (input.hasNext())   // assumes each question has an answer
      {
          myQuestions.add(input.nextLine());
          myAnswers.add(input.nextLine());
      }
   }
   
   catch (IOException e)
   {
       System.out.println("Error reading file " + filename);
       System.out.println(e);            
   }
}

Problem 4 Part C.2
      
   public void createQuestion()
   {
      int num = myGenerator.nextInt(myQuestions.size());
      setQuestion(myQuestions.get(num));
      setCorrectAnswer(myAnswers.get(num));
   }