# CSC 2200 Lecture Notes - Lecture 24: Shellsort, Sorting Algorithm, Insertion Sort

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19 Jul 2018

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CSC 2200 lecture 24

Shell sort

•Shell sort is a highly efficient sorting algorithm and is based on

insertion sort algorithm.

•This algorithm avoids large shifts as in case of insertion sort, if the

smaller value is to the far right and has to be moved to the far left.

•This algorithm uses insertion sort on a widely spread elements, first

to sort them and then sorts the less widely spaced elements.

•This spacing is termed as interval

Shell sort

•This interval is calculated based on Knuth's formula as −

h = h * 3 + 1 where h is interval with initial value 1

•This algorithm is quite efficient for medium-sized data sets as its

average and worst case complexity are of Ο(n), where n is the number of items.

How Shell Sort Works?

•Let us consider the following example to have an idea of how shell

sort works.

•We

take the same array we have used in our previous examples.

•For our example and ease of understanding, we take the interval of 4.

•Make a virtual sub-list of all values located at the interval of 4positions.