Class 51: An Introduction to Sorting

Held: Wednesday, 30 November 2005

Summary: Today we begin to consider the problem of Sorting, putting elements of a collection in order, typically from smallest to largest. Sorting is one of the fundamental problems of computing.

Related Pages:

• EBoard.
• Sample Code.

Notes:

• It's time for me to decide whether or not to have a textbook next semester. What do you think?
• Are there questions on Exam 3? I'll give each of you a chance.

Overview:

• The problem of sorting.
• Carefully specifying that problem.
• Testing a sorting method.

Sorting

• Sorting is the problem of putting the elements of a collection in order.
• There are a variety of ways to express the problem of sorting.
  • What kind of collections do we sort? Typically arrays, vectors, and lists.
  • Do we return a new, sorted, collection, or do we sort "in place" (changing the parameter collection)?
  • How do we compare elements?
    • Using the "normal order" for the objects (as governed by the compareTo method)
    • Using an external comparator
  • If we use an external comparator, how do we obtain it?
    • As a field of the class that does the sorting
    • As a parameter to the sort method
• For most of our study, we will sort vectors in place with a separate comparator field.

Specifying Sorting

• How do we specify the problem of sorting?

Testing

• How would we test a sorter? We'll develop an answer.