Continue partners.

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Short pre-brief
• Lab
• Debrief (if time)

Preliminaries

Admin

• Project sketches due!
  • I plan to comment on your proposals and sketches tonight.
• Quizzes likely returned tomorrow. (I had four hours reserved for work this a.m.; three got used for administrative work.)
• Reminder: Review sessions on Wednesday and Thursday!

Upcoming Work

• No lab writeup.
• Reading for Wednesday:
  • Association Lists
• Part two of the project due next Tuesday.
• Nothing due the week after Turkey break.
  
  • We may distribute exam 4 next Wednesday for those who want to use break time to work on the exam. But it will be designed as if we distributed it immediately after break.

Extra Credit Opportunities

Academic

• CS Extras Thursday: Text Recognition in Maps
• CS Table Friday: One Year After Healthcare.gov
• CS Extras Tuesday the 25th: Summer Opportunities in CS

Peer Support

• Karan's radio show 11pm Thursday nights on KDIC
• Evan's radio show 5pm Friday nights on KDIC
• Donna's radio show Sunday midnight on KDIC
• One acts, coming soon
• Swimming and Diving at Loras on Saturday

Miscellaneous

• SHACS Open House, Today, 4-5pm. "If you have nay questions or concerns about the changes in SHACS, come to their open house."
• VP Student Affairs Candidate Open Sessions
  • Wednesday, 4:15, JRC 209
  • Friday, 4:15, JRC 209

Questions

Prebrief

Key points of the reading?

• Procedures can be more or less efficient.
• We should try to make our procedures more efficient.
• We can figure out efficiency by counting steps (e.g., number of calls)
• We can use vectors to implement those counters.

What was confusing?

Using counters makes sense, but I don't get how they work

We set up one counter per procedure.

That means we need things that change.

Vectors allow us to change. Each counter is a one element vector where the element is the count (of calls to the corresponding procedure).

    (vector-set! vec 0 (+ 1 (vector-get! vec 0)))

Once you know how to do something, you don't rewrite the complex code, you name it as a procedure. counter-increment!

I don't get the difference between linear time and constant time

Terms for efficiency.

Linear time: You do a number of calls approximately proportional to the size of input elements (e.g., the number of elements in a list).

Constant time: Independent on the size of the input. car takes only one step, whether it's 100 elements or 1000 elements or 10000000 elements.

Explain all of the counter-x procedures. How do we integrate them

Setup: Outside the procedure

    (define PROC-counter (counter-new "procedure"))

    (define member?-counter (counter-new "member?"))

Setup: Inside the definition of the procedure

    (counter-increment! PROC-counter)

    (define member?$
      (lambda (val lst)
        (counter-increment! member?-counter)
        (and (not (null? lst))
             (or (equal? (val (car lst)))
                 (member?$ val (cdr lst))))))

Analysis

    (counter-reset! member?-counter)
    (member?$ 1000 (iota 1000))
    (counter-print! member?-counter)

    (counter-reset! member?-counter)
    (member?$ -1 (iota 1000))
    (counter-print! member?-counter)

Lab Reflections

• One more extra credit thing: SHACS open house today, 4-5pm.
• Did you think about why one version of reverse took so much more time? Did you try a larger list?