CSC 207.01 2019S, Class 34: Chaining in hash tables

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Extra credit
  • Questions
• Lab

Preliminaries

News / Etc.

• Reminder: Next week’s Science Teaching and Learning Group will discuss student wellness. I’m hoping to share some of the extra credit reports you’ve submitted (anonymously). Let me know if you object to me sharing yours.

Upcoming work

• Reading for Monday: Forthcoming.
• Today’s lab writeup: Exercise 5c. (Class 34)
• Exam 2 due next Thursday.
  • Prologue due Monday night.

Extra credit

Extra credit (Academic/Artistic)

• CS Table, next Tuesday, Facebook Data
• Three talks by Prof. Dr. Yvonne Foerster (https://yvonnefoerster.com/)
  • Wednesday: May 1, 4:30-6pm, HSSC S3325: Beyond the Anthropocene: Technology, Innovation, and the (Post-)Human Condition
  • Thursday, May 2, Noon-12:50pm, HSSC N3110 Degrees of Freedom: Embodiment, Neuroplasticity, and the Need for a Critical Neuroscience (Lunch and beverages provided)
  • Friday, May 3, Noon-12:50pm, Bucksbaum 152: Designing Future Bodies: Fashion and Technology (Lunch and beverages provided)

Extra credit (Peer)

• Today: Contra tonight at 8pm in Loose (live band + live caller)
• Today: Track at Grand View
• Tomorrow: Titular head

Extra credit (Wellness)

• Guided Movement Meditations, 12:15 Friday and Saturday, Flanagan Theatre. Also between performances of the show.
• Hand-made nodel workshop tonight.

Extra credit (Wellness, Regular)

• 30 Minutes of Mindfulness at SHACS/SHAW every Monday 4:15-4:45
• Any organized exercise. (See previous eboards for a list.)
• 60 minutes of some solitary self-care activities that are unrelated to academics or work. Your email reflection must explain how the activity contributed to your wellness.
• 60 minutes of some shared self-care activity with friends. Your email reflection must explain how the activity contributed to your wellness.

Extra credit (Misc)

• CS Picnic Next Friday! (Info forthcoming.)

Other good things

Friday PSA

• I want you to be happy and healthy, take care of yourselves.

Questions

Do you have a recommended strategy for detecting concurrenct modifications?

In the main structure, keep a counter of the number of modifications.

Each time you create an iterator, copy that counter.

Each time you modify in the struture, update the counter in the structure.

If the iterator’s counter does not match the structure’s, we have a concurrent modification, and should throw and exception.

Each time you modify in an iterator, update the counter in both the structure and the iterator.

This approach is unlikely to be thread safe. Take OS to find out what that means.

Lab

How did you figure out that anteater and buffalo map to the same cell in the hash table?

Experimentation. (That is, I made a large list of animal names and tried to add each until I got a collision.)

What should get do if the key is not there?

It should throw an IndexOutOfBoundsException.

_How would you suggest we iterate the arraylist in get?

    for (Pair<K,V> pair : alist) {
      ...
    } // for

_Why not with for (int i = 0; i < alist.size(); i++) { ... }?

The first is easier to read. It’s also easier to use if we decide to change how we represent buckets.

_How would you suggest we iterate the ArrayList in set?

For that, you likely need the for (int i ...) pattern.

Why?

So that you can more easily replace the element if you find a match.

What’s today’s lab writeup?

Exercise 5c. (This is Class 34)