Added Shell Sort

Sorting/Shell Sort/README.md

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+# Package/Script Name
+
+## Aim
+
+The main aim of the script is to sort numbers in list using shell sort.
+
+
+## Purpose
+The main purpose is to sort list of any numbers in O(n^2) time complexity.
+
+
+## Short description of package/script
+
+In shellSort, we make the array h-sorted for a large value of h. We keep reducing the value of h until it becomes 1. An array is said to be h-sorted if all sublists of every h’th element is sorted.
+
+
+## Workflow of the Project
+
+Gap is reduce by half in every iteration. 
+In this case, we begin with n2n2 sublists. On the next pass, n4n4 sublists are sorted. Eventually, a single list is sorted with the basic insertion sort.
+
+## Setup instructions
+
+Install latest version of python from [python](https://www.python.org/downloads/)
+
+
+## Compilation Steps
+
+Open editor and open the file and compile the program and give input and get the desired output.
+
+
+## Sample Test Cases
+<h3>TEST CASE-1</h3>
+<h4>Input:</h4>
+1 98 3 16 3
+<h5>Output:</h5>
+1 3 3 16 98
+
+<h3>TEST CASE-2</h3>
+<h4>Input:</h4>
+5 4 3 2 1
+<h5>Output:</h5>
+1 2 3 4 5
+
+<h3>TEST CASE-3</h3>
+<h4>Input:</h4>
+1 1 1 0 0
+<h5>Output:</h5>
+0 0 1 1 1
+
+## Output
+
+![](https://github.com/thejaswin123/PyAlgo-Tree/blob/main/Sorting/Shell%20Sort/Images/shell_sort.png)
+
+## Author(s)
+
+[Thejaswin S](https://www.github.com/thejaswin123)
+

Sorting/Shell Sort/shell_sort.py

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+''' This program illustrates the shell sort implementation in Python
+
+ Shell sort or Shell's method, is an in-place comparison sort.
+ It can be seen as either a generalization of sorting by exchange (bubble sort) or sorting by
+ insertion (insertion sort). The method starts by sorting pairs of elements far apart from each other,
+ then progressively reducing the gap between elements to be compared. Starting with far apart elements
+ can move some out-of-place elements into position faster than a simple nearest neighbor exchange.
+
+ Best Case O(n logn); Average Case O(depends on gap sequence); Worst Case O(n^2)'''
+
+
+
+def shell_sort(arr): #function for shell sort
+ sublistCount = int(len(arr)/2) 
+
+ while sublistCount > 0:
+ for start in range(sublistCount):
+ do_insertsort_gap(arr,start,sublistCount)
+ sublistCount = int(sublistCount/2) 
+ return arr 
+
+def do_insertsort_gap(arr,start,gap):
+ for i in range(start+gap,len(arr),gap):
+ currentValue = arr[i]
+ position = i
+ while position >= gap and arr[position-gap] >= currentValue:
+ arr[position] = arr[position-gap] # We compare values in each sub-list and swap them (if necessary) in the original array.
+ position = position-gap
+ arr[position] = currentValue 
+
+array = input("Enter the elements of the array separated by space : ") #Taking input
+array = [int(x) for x in array.split(" ")] #string to int conversion
+
+print(f"Array after sorting is : {shell_sort(array)}") #printing the output
+
+
+# sample Test case 
+""" >>> shell_sort([0, 5, 3, 2, 2])
+ [0, 2, 2, 3, 5]
+ >>> shell_sort([])
+ []
+ >>> shell_sort([-2, -5, -45])
+ [-45, -5, -2]
+ """