Overview

• Preliminaries.
  • Admin.
  • Questions on the project.
• The problem of sorting.
• Writing sorting algorithms.
• Examples.
• Formalizing the problem.

Preliminaries

Admin

• Welcome to any prospectives visiting with us today!
• There is no lab writeup for today.
  • There is, however, a quiz today.
  • And a reading for tomorrow.
• We have added an 11 am section of 161. However, only 18 people have no conflicts at that time. If you are taking 161 and can switch to 11, I would encourage you to do so during add/drop period.
• I may be sending out more grades tonight.
• Note: When grading lab writeups, I
  • Look in the folder where I file writeups when I arrive
  • Search in my mailbox for all the mail meeting the title of the lab
  • Search in my mailbox for all mail from people who don't seem to have submitted the lab
  • If I don't find your lab writeup after all of that, I have to assume that you have not submitted it.
  • So it really helps if you follow the naming conventions
• Upcoming extra credit opportunities:
  • "Data Sovreignty: The Challenge of Geolocating Data in the Cloud", November 25, 4:15 JRC 101
  • Showing of "Gold Fever" by Andrew Shurburne '01 or so, 7:00 p.m. Monday, November 25, ARH 302
  • Tuesday, November 26, 4:15 p.m., JRC 209 a gaming event with the game [d0x3d!] Popcorn will be served.
  • Any self-care week event during what I refer to as purgatory week.

Questions on the Project

• Yes, you have a different due date than the other section. Tuesday after Turkey break.
• Yes, you can apply the notes I gave you.
• No, you don't have to cite ideas.

The problem of sorting

• Goal: To put things in order.

Writing sorting algorithms

• Yay! A class exercise.
• Attempt it by hand
• Attempt to formalize
• Attempt to verify
• Attempt to turn into code

Examples

• Letter sort - Bucket Sort [3 groups]
  • Find all of the A's
    • Then sort all of the A's.
  • Find all the B's
    • Then sort all of the B's.
  • For the recursive sorts, we use the next positions
  • ...
  • This can be relatively fast, if implemened correctly.
  • Need a way to break into categories.
• Bubble sort [3 groups]
  • Go through the list once, swapping out of order elements
  • Do it again and again and again ...
  • Sam's least favorite sorting algorithm
• Insertion sort [5 groups]
  • One by one, take cards from the original list and put them in "the correct place" in the second list
• "Binary sort"
  • Split the deck into two halves, small and large
  • Sort each half
  • Shove 'em back together
• Selection sort [1 group]
  • Repeatedly
    • Find the smallest remaining value
    • Add it to a new list
• Permutation sort
  • Make every permutation of the list
  • Decide which one is sorted

How would you choose which one to implement?

• Most efficient
  • Bucket, then "Binary" (Quicksort)
• Easiest to get right
  • Bubble
  • Selection
• Not bubble sort, because Sam will fail you

Formalizing the problem