Shell sort is a generalization of insertion sort that improves performance by sorting elements with gaps between them. It works by first sorting elements with a large gap between them, then reducing the gap and sorting again until the gap is 1. For example, with an array of 8 elements and an initial gap of 4, elements are first sorted in groups of 4 apart, then with a gap of 2, and finally with a gap of 1 to fully sort the array. The algorithm uses this gap sequence: n/2, n/2, n/2, ..., 1.

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Name Nauman Ali
Class BS CS 3
ReG # 024
Indroduction

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PROJECT NAME

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Shell Sort – Basic idea
generalization of insertion sort
Create a gap by half the number of array.
Compare the elements and sort.
Repeat sorting until gap become equal to 1.
For gap Donald Knuth..
Start with h = 1
h = 3*h + 1
h > n
h = (h – 1) / 3

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Shell Sort - example
8 2 5 34 67 1
Total numbers of element 8.
Initialy Gap = 4
7 1 3 54 68 2

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Shell Sort - example (2)
7 2 5 34 68 1
Gap =4/ 2
Gap=2
3 1 5 82 67 4

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Shell Sort - example (3)
1 2 3 74 85 6
3 1 5 82 67 4
Gap = 2/2
Gap=1

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Shell sorting code
for( gap=n/2; gap>0; gap/=2)
{
for( i= gap; i<n; i++ )
{
temp=array[i];
for(j=i; j>=gap && array[j-gap]>temp ; j - = gap)
{
array[j]=array[j-gap];
}
array[j]=temp;
}
}
N=8
Gap = 4

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references
Youtube and
en.wikipedia.org/wiki/Shellsort

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