These are my quick notes on exam 2. They are not intended to be comprehensive; it's mostly a collection of things I noted that you might also want to note. I may be making my solutions available in the near future.

Distribution of unit test results

• Problem 1: 18 passed, 4 failed
• Problem 2: 14 passed, 5 failed both test suites, 3 failed only remove
• Problem 3: 11 passed, 11 failed
• Problem 4: 6 passed, 13 failed, 3 did not terminate

Some general notes

Please be more careful about citations! It's not a minor issue. For your sanity, incorrect with citations is better than correct with no citations.

Once again, I was a bit more generous on bad formatting than I should have been. People who regularly violated formatting standards lost a point (rather than having their exams rejected). People who only violated formatting standards on one problem (a bid odd, in my pespective) usually lost 1/2 point. People who ocasionally violated formatting standards may have lost partial credit.

There were also a number of other programming problems: Uncommented fields and methods, fields in the wrong place (e.g., in the methods section), incorrect capitalization, etc. Again, I may not be so sympathetic in the future.

A surprising number of you used private as a modifier for fields and methods. Since I almost never use private, I'm wondering where you developed the habit. (I generally recommend against private; it's often useful for subclasses or friendly classes to be able to access your fields and methods.)

I hope to never again see anything like the following code

if (pred.test(param))
  return true;
else
  return false;

I also hope to never see anyting like the following code

if (pred.test(param) == true)
  ...;

There were fewer explicit loop invariants than I would have liked, and some of the ones that were there were careless enough that they were unlikely to be helpful.

Many of you need to start the next examination sooner.

Notes on Individual Problems

Problem 1

If your code passed the tests, but wasn't O(nlogn), you were unlikely to receive credit. (See last Friday's CS table.)

People who changed the meaning of the parameters in the helper but did not change the documentation also likely lost credit.

Problem 2

This problem had more private fields (which were often uncommented, badly placed, and inconsistently initialized) than any other.

Problem 3

A few of you chose to implement methods that were already implemented (e.g., add and remove). The goal was really to find a way to wrap those methods appropriately. (In this case, you did need to access the underlying data structure for the next and hasNext methods.)

Problem 4

A few of you implemented this by passing integer indices to the partition method and then advancing the iterator to those indices. But if you do that for each recursive call, your procedure is no longer O(n). The partition method needs to take the iterators as parameters.