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Insertion Sort algorithm in Python

Insertion Sort algorithm in Python

Hello everyone, welcome back to programminginpython.com. Here am going to tell you how to implement Insertion Sort Algorithm in Python. In the previous posts, I have said about Merge Sort, Selection Sort, and Bubble Sort, here I will show you Insertion Sort which is more efficient than Selection and Bubble sort techniques.

Insertion Sort is an in-place sorting algorithm. Here a sub-list is maintained which always sorted, as the iterations go on, the sorted sub-list grows until all the elements are sorted. In each iteration, an element in the main list(unsorted list) is picked and placed correctly in the sorted list by shifting elements to the right which are greater than the element picked from the unsorted sub-list.

You can also watch the video on YouTube here.

Program on GitHub

See the below animations,

By Swfung8Own work, CC BY-SA 3.0, Link

By Simpsons contributorOwn work, CC BY-SA 3.0, Link


Time Complexity Of Insertion Sort

Best Case O(n2)
Average Case O(n)
Worst Case O(n2)

Program on GitHub

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Given a list L of n elements with values or records L0, L1, …, Ln-1.

  1. Initially, L0 is the only element in the sorted sub-list.
  2. Compare L1 with the elements in the sorted sub-list(initially L0 and L1), and place it in the correct position(shift all the elements in the sorted sub-list that is greater than the
    value to be sorted)
  3. Repeat the same step until Ln-1


__author__ = 'Avinash'

def insertion_sort(sort_list):
    for i in range(1, len(sort_list)):
        key = sort_list[i]
        j = i - 1
        while j >= 0 and key < sort_list[j]:
            sort_list[j + 1] = sort_list[j]
            j -= 1
        sort_list[j + 1] = key
    print('\nThe sorted list: \t', sort_list)

lst = []
size = int(input("\nEnter size of the list: \t"))

for i in range(size):
    elements = int(input("Enter the element: \t"))


Program on GitHub


Insertion Sort Algorithm in Python
Insertion Sort Algorithm in Python

Also, feel free to look at other sorting algorithms like Bubble Sort or Selection Sort and searching algorithms like Linear Search and Binary Search.

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