CSC151 2009F, Class 47: Insertion Sort

Admin:
* Reading for tomorrow: Merge Sort.
* Projects have started to arrive.  Yay!  
  * In a number of cases, I've suggested that folks review the 
    grading rubric for the project.  
  * (Don't lose those easy points, folks!)
* We'll strive for ten minutes of lecture/discussion followed by lots of 
  lab time.
* EC for
  * Watching some unnamed track coaching Grinnell alum on Jeopardy at 
    3:30 today
  * Womens basketball (looking ahead)

Overview:
* What is the key idea of insertion sort?
* Why do we have multiple versions of insertion sort?
* Lab

Sorting: Goal is to put a collection in order
* We have different representations of collections:
  * vectors
  * lists
* We think about sorting lsits and sorting vectors differently
  * lists are immutable, so when we sort a list, we build a new list
  * vectors are mutable, so we often sort "in place"
* Yesterday: Different techniques for sorting, often with a key
  idea
  * First technique: Shift elements until they seem to be in the
    "right" position  "Shifty sort"
  * Second technique: Select the smallest remaining element and put
    it at the front
* Today: Another technique: Insertion sort, starting with lists
  * Repeatedly insert elements into an expanding sorted list

* Reading gave four versions of insertion sort
  * numbers-insertion-sort
    * Easier to understand
  * list-insertion-sort
    * A straightforward generalization
  * list-keyed-insertion-sort
    * Working with a list of lists, and we want to sort by one
      part of the compound values
      * E.g., a list of (name/phone-number/fave color) triples,
        and we want to sort by phone number
  * vector-insertion-sort!
    * Everything else works on lists, we need at least one thing
      to sort vectors