Python: Shell sort

Python Search and Sorting: Exercise-7 with Solution

Write a Python program to sort a list of elements using shell sort algorithm.
Note : According to Wikipedia "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."

Sample Solution:

Python Code:

def shellSort(alist):
    sublistcount = len(alist)//2
    while sublistcount > 0:
      for start_position in range(sublistcount):
        gap_InsertionSort(alist, start_position, sublistcount)

      print("After increments of size",sublistcount, "The list is",nlist)

      sublistcount = sublistcount // 2

def gap_InsertionSort(nlist,start,gap):
    for i in range(start+gap,len(nlist),gap):

        current_value = nlist[i]
        position = i

        while position>=gap and nlist[position-gap]>current_value:
            position = position-gap


nlist = [14,46,43,27,57,41,45,21,70]

Sample Output:

After increments of size 4 The list is [14, 41, 43, 21, 57, 46, 45, 27, 70]                                   
After increments of size 2 The list is [14, 21, 43, 27, 45, 41, 57, 46, 70]                                   
After increments of size 1 The list is [14, 21, 27, 41, 43, 45, 46, 57, 70]                                   
[14, 21, 27, 41, 43, 45, 46, 57, 70]


Flowchart: Python Data Structures and Algorithms: Shell sort

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Next: Write a Python program to sort a list of elements using the merge sort algorithm.

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Python: Tips of the Day

Use Reversed() In for Loops:

>>> tasks = ['laundry', 'picking up kids', 'gardening', 'cooking']
>>> for task in reversed(tasks):
...     print(task)
picking up kids