Straight selection sort vs. exchange selection sort

Question

What is the difference between straight selection sort vs. exchange selection sort? I got into a little debate today - my professor uses these two terminologies in his lecture notes. The selection sort that Wikipedia and any textbook or website will give you is what he is calling "exchange selection sort".

I've never heard the term "exchange selection sort" used before (only "selection sort"), and cannot find any relevant resources on the former terminology online. Also, "exchange sort" redirects to bubble sort on Wikipedia.

I've also never heard the term "straight selection sort" used before, and cannot find any relevant resources online. His notes state that it's a version of selection sort which uses a secondary array rather than an in-place sort, populating it one-by-one from the smallest to largest element. When I brought up the issue he claimed it was older and that just because it doesn't come up on Google doesn't mean it's incorrect. However, I've found far more obscure things on Google, and something like selection sort is going to have a massive amount of resources on the web.

So, do these algorithms go by other names? Does he simply have the names wrong? Who is right?

Answer 1

I hadn't heard those exact terms before but they make sense to me. I don't think the terminology is really that important as long as you understand what they're doing.

If you're creating a sorted copy of a list, you can create each item in the new list one-by-one from the minimum of the old list; ‘straight’ seems as reasonable a description as any for this.

OTOH if you're sorting a list in-place then each time you move a new item to the head of the list, you have to move the item that was previously there backwards to make room. In an array list the cheapest way to do that is just to left the new minimum item and the old item swap places: an exchange. (In a linked list it would be quicker to let the whole tail of the list slide back one place.)

Textbooks tend to concentrate on in-place sorting.