CSC302 2007S, Class 09: Representing Drawings

Admin:
* PLEASE DO YOUR BEST TO SHOW UP ON TIME!
* Assigned: HW4.
* Does anyone read the responses I write to your questions?
* There are three readings for Monday.  
  Make sure to respond to each of them separately.
* Next Friday at lunchtime, Atul Gupta '88 or so, will be 
  speaking about programming in the real world and about internship
  opportunities at his company.
* Due: HW3.

Overview:
* Lab.

/HW3 - An alternate exponentiation strategy/

(0) let accumulator = 1;	// O(1)
(1) while n != 0		// O(log2n) repetitions
(1a) find the largest m such that 2^m <= n // O(log2n)
    (simultaneously find x^m)
(1b) let accumlator = accumulator * x^m // O(1)
    let n = n - m
(2) return accumulator

If the two O(log2n) assumptions are correct, what is the running time?
* O((log2n)^2)
* log2n * log2n = (log2n)^2

/Quicksort - How did you test/

* Generate some random arrays, print them out, sort them, print the results, and check
* Didn't bother - I took (and cited) Sam's code, and Sam's code is always correct.
  * And I have a bridge to sell you.
* I modified code I wrote before, and I would not have submitted
  incorrect code.
  * Manual command line testing

What technique should you be using?
* One possibility: Write a procedure that checks (a) that the
  result is sorted and (b) that the result is a permutation of
  the input  O(n^2ish)
* Use the stuff you learned in 201