Comparisons Required
To merge two sorted lists, each with about N/2 elements, into a sorted list with N elements takes at most N-1 comparisons
Therefore, if you were to use one of our earlier sorts to sort the two halves, it would take about
(N/2)^2 + (N/2)^2 + N ~ N^2 / 2 comparisons
Therefore, we have saved about 1/2 the work.
However, we can do even better if we use the merge sort to sort the two halves.