In Lesson A17, Quadratic Sorting Algorithms, we saw how the number of steps required increased N² when sorting N elements. In this lesson, we will study a recursive sort, called mergeSort that works by dividing lists in half. After solving a preliminary merge problem, you will code a recursive mergeSort.

The key topics for this lesson are:

1. Non-Recursive MergeSort
2. A Merge Algorithm
3. Recursive MergeSort
4. Order of Recursive MergeSort