Computer Science APEA 15-100, Summer 2009
Homework 9
Due:  Wed 15-Jul-2009 at 8:59am (email copy only)
(no late submissions accepted).

Read these instructions first!

• Now you are not given a file to start from!  Based on previous hw's, create your own Hw9.java file.  Be sure to name it exactly correctly, to include a main method that calls checkAssertsAreEnabled and testAll, and to have testAll call suitable test methods for all the methods you create.  Also, be sure that every method you write has exactly the right name and the right signature.
   
• Be sure to include your name, your Andrew ID, and your section clearly on the top of each file in your assignment.
   
• For non-programming problems:
  • Place all your solutions to the non-programming problems in a single file named Hw9 (with whatever extension is appropriate for the format you choose, such as Hw9.txt or Hw9.html, etc).  You must use one of these file formats: plain text (txt), or RTF, or HTML, or Word (doc, not docx), or PDF.  No other file formats will be accepted.
  • Show your work.  Correct answers without supporting calculations will not receive full credit.
     
• For programming problems:
  • Try to use well-named variables, proper indenting, reasonable commenting, etc.
  • Note:  You may not use Java concepts we have not yet covered, including loops (do/while/for), conditionals ("if" statements or tertiary operators (?:)), arrays, or methods from any classes in java.util.* (besides Scanner or others we explicitly use) to solve these problems (which isn't a problem for most of you, seeing as we have not yet covered these!).  While they may be helpful, every problem here is solvable without them, and they are not permitted for now.
     
• What to submit
  • Create a submission directory like this:  "koz-hw9"  (replace "koz" with your andrew id)
  • Place all the files you are submitting in that directory, zip that directory, and submit the zipped directory
     
• How to submit
  • Send an email with the zipped submission directory as an attachment to your CA by the submission deadline.  Do not miss the deadline, even by one minute!  Email problems are not a valid excuse for late submissions.
  • It is recommended that you "cc" yourself in that email, too, just to confirm that you properly sent the email.
     
• Note:
  • Improper submissions will be penalized up to 10 points and may be rejected.
  • Late submissions will be rejected.

1. Finish Lab 9
2. dotProduct
3. rotate
4. finalPosition

1. Finish Lab 9
   Finish all the examples from lab 9.  Include the solutions in your submission, all in one file named Lab9.java.  Note: the lab collaboration policy continues to apply to the lab problems.  So you can collaborate at will to solve these problems.  This only applies to the lab problems -- all other problems in this assignment are subject to the usual homework collaboration policy.
    
2. dotProduct
   Write the following method:
      public static int dotProduct(int[] a, int[] b)
   This method takes two (possibly-null) arrays of int's and returns the dot product of those two arrays.  If this is not possible, the method returns -1.  For more info, see the Wikipedia page on dot products.  Write your own test method.
    
3. rotate
   Write the following method:
      public static int[] rotate(int[] a, int n)
   This method takes a (possibly-null) array of int's "a" and an int "n", and returns a new array which is the result of rotating the elements in the original array n places to the right with wraparound.  So, for example, if "a" equals { 1, 2, 3, 4, 5 }, then rotate(a,2) would return the array { 4, 5, 1, 2, 3 }.  If "a" is null, the method should return null.  Write your own test method.
    
4. finalPosition
   Write the following method:
      public static int[] finalPosition(int[] dirs)
   This method takes a (possibly-null) array of int's representing directions (where  UP is 1, DOWN is 2, RIGHT is 3, and LEFT is 4), and returns the (x,y) coordinates that results from starting at the origin and following each of these directions in sequence.  So, if the array contains { 1, 3, 2, 3 }, this indicates to start at (0,0), go up to (0,1), right to (1,1), down to (1,0), and right to (2,0).  These values are returned in an array, so the result would be the array { 2, 0 }.  If  the "dirs" array is null, the method should return null.  Write your own test method.

Carpe diem!