Modify the mergesort algorithm to remove duplicates in the merging step to obtain an algorithm that removes duplicates from an array. Note that the resulting array does not have the same ordering as the original one. What is the efficiency of this algorithm?

A stable sort does not change the order of elements with the same value. This is a desirable feature in many applications. Consider a sequence of e-mail messages. If you sort by date and then by sender, youd like the second sort to preserve the relative order of the first, so you can see all messages from the same sender in date order. Is selection sort stable? Insertion sort? Why or why not?