Mergesort. Merge left, merge right, merge.
Merge. Understand how to carry out the merge operation. How many compares does it use when comparing two arrays of size N in the best case? In the worst case?
Mergesort order of growth. Understand how to show that the order of growth of the number of compares is N lg N. Understand why the entire algorithm is also order N lg N.
Mergesort compare bounding. Know why the best case is ~ 1/2 N lg N and the worst case is ~ N lg N compares.
Mergesort properties. Mergesort is stable (why?). Mergesort uses N extra memory (why?). Does mergesort do particularly well on already sorted arrays? Partially ordered arrays?