EBoard 22: Searching

Warning This class is being recorded. At least I think it is. It’s probably also being transcribed.

Approximate overview

• Administrivia
• The Beginner’s Creed
• Questions
• Lab

Administrivia

• Beware! Friday the 13th falls on Friday this month.
• Friendly reminder: Treat your partners with respect.
• Unfortunately, our mentors will not be here today.

Upcoming Token activities

Academic

• Today: Talk and movie on security (1pm, Strand 3). https://forms.office.com/r/u34bDgj8w2

Cultural

Peer

• Football, 1pm Saturday, 21 October 2023.

Wellness

• Be well during fall break.

Misc

• Watch the eclipse (but don’t stare directly at it)

Other good things (no tokens)

Upcoming work

• Saturday: MP5
• Sunday night: MP5 post-assessment
• Break: Nothing (or LAs, or MP redos, or …)

The Beginner’s Creed

http://denninginstitute.com/pjd/PUBS/CACMcols/cacmJul17.pdf

I am a beginner.
I am entering a new game about which I know nothing.
I do not yet know how to move in this game.
I see many other people playing in this game now.
This game has gone on for many years prior to my arrival.
I am a new recruit arriving here for the first time.
I see value to me in learning to navigate in this domain.

There is much for me to learn:
The basic terminology
The basic rules
The basic moves of action
The basic strategies

While I am learning these things I may feel various negative reactions:
Overwhelmed at how much there is to learn
Insecure that I do not know what to do
Inadequate that I lack the capacity to do this
Frustrated and discouraged that my progress is so slow
Angry that I have been given insufficient guidance
Anxious that I will never perform up to expectations on which my career depends
Embarrassed that everyone can see my mistakes

But these moods are part of being a beginner. It does not serve my goal and ambition to dwell in them. Instead,
If I make a mistake, I will ask what lesson does this teach.
If I make a discovery, I will celebrate my aha! moment.
If I feel alone, I will remember that I have many friends ready to help.
If I am stuck, I will ask for help from my teachers.

Over time, I will make fewer mistakes.
I will gain confidence in my abilities.
I will need less guidance from my teachers and friends.
I will gain familiarity with the game.
I will be able to have intelligent conversations with others in the game.
I will not cause breakdowns for promises that I lack the competence to keep.
I have an ambition to become competent, perhaps even proficient or expert in this game. But for now,
I am a beginner.

—By Peter J. Denning From Communications of the ACM 60(7), July 2017

Questions

Lab

Sam’s reflections:

• The looped test is good at catching errors. I’ve seen student code fail exactly one of the 1024-or-so tests.
  • Rather than writing individual tests, it’s nice to write procedures that generate lots of tests.
  • The output from your test can help you analyze your code.
• Detour: Famous error: Find the midpoint with (lb + ub)/2;
  • Solution: lb + (ub-lb)/2;
  • Mathy explanation
    • (lb + ub)/2 = lb/2 + ub/2
    • lb + (ub-lb)/2 = lb + ub/2 - lb/2 = lb - lb/2 + ub/2 = lb/2 + ub/2
• Debugging is your friend.
• Although, intuitively, we want “half the array” in binary search, we cannot use arrayCopy to get half. That turns our efficient O(logn) algorithm into an O(n) algorithm.