Merge sort as folk dance
Written by Mike James
Sunday, 24 April 2011

The sort of the dance has now reached Merge Sort and it's very tricky - how does it end up with the boy-girl pairing?

Yes the team from Sapientia University is still dancing sort algorithms but no sign of a Quicksort just yet, even though it has been promised. If you would like to see their original four sorting dances then see Sorting algorithms as dances. This time we have a merge sort for you to follow.

In a Merge store the list is recursively divided into two lists until you reach a list consisting of one element (dancer) and then each list is merged to produce a list twice its size by taking the the elements from pairs of sub-lists in order. So if you have two lists [5] and [3] you take the 3 and then the 5 to give the list [3,5]. If you then have two lists [3,5] and {2,8] you take the 2 from the second list, then the 3 from the first list, then the 5 from the first and the 8 from the second to give [2,3,5,8] and so on.

The merge is much easier to see when you have two big partially sorted lists which is what happens near the end of the dance when the boys merge with the girls - how was that worked out! And more to the point how is it that in the final merge each boy ends up with a girl?

Ah such is the complexity and surrealism that is the sort of the dance....

If you would like to find out the details of merge sort from a programmer's perspective then see: Magic of Merging.

We wait patiently for the Quicksort but still don't think it is danceable....

#### Update 2nd May 2011

They have proved me wrong .... all it need for Quicksort as a Hungarian dance is a pair of hats:
At last - Quicksort the dance

#### Further Reading:

Sorting algorithms as dances

Silverlight Sorting Lab

SilverSort

Magic of Merging

QuickSort exposed

Sequential storage

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Last Updated ( Tuesday, 03 May 2011 )