Comments on: Computer Algorithms: Shell Sort

By: Stephanie

Stephanie — Tue, 11 Jul 2017 12:32:14 +0000

i’m confused by the implementation piece. You talk about the Knuth algorithm which is (3^k-1)/2 but in your second implementation of shell sort you essentially only divide the number of elements by 2. What am I missing?

By: Mohammad Fakhreddin

Mohammad Fakhreddin — Thu, 17 Dec 2015 20:58:33 +0000

It was really helpful thanks.

By: Yang

Yang — Mon, 17 Mar 2014 22:30:43 +0000

Can I say that the shell sort just reduce the # of swaps but # of compares is more than the insertion sort?
Because I think even if the input is sorted, the algorithm needs to compare the sequence once when gap = 1, and when we calculate the other gaps, the # of compares must increase.

By: Mateusz

Mateusz — Mon, 15 Oct 2012 16:13:12 +0000

The images give the impression that every i’th number is compared in shell sort and then swapped if necessary.

The image presents the algorithm the following way:
If the gap is 3:
For all elements in the array compare only every third numbers,

Where the Shell Algorithm says:
If the gap is 3:
for every x in the array:
compare x with y (which lies 3 items ahead)

This video shows how the algorithm works:
http://www.youtube.com/watch?v=qzXAVXddcPU