Merge Sort Algorithm in Python

Hello everyone, welcome back to programminginpython.com. Here in this post am going to tell you how to implement Merge Sort Algorithm in Python. In the previous posts, I have said about Selection Sort and Bubble Sort, here this Merge sort is much more efficient than those two algorithms as their time complexity is O(n2) in average case and here it is O(n log n) in worst case, this says how efficient Merge sort is than Selection and Bubble sort.

Merge sort algorithm is a divide and conquer algorithm, where the main unsorted list is divided into 2 halves and each of the halves is again divided into 2 halves until only single element is left in the list. Now merging these sublists by sorting them and finally the main list is sorted.

You can also watch the video on YouTube here

Program on Github

See the animation below,

Merge Sort Algorithm - programminginpython.com

By Swfung8Own work, CC BY-SA 3.0, Link

Time Complexity Of Merge Sort

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

Algorithm

  1. Divide the unsorted list into n sublists, until each list has only 1 element (a list of 1 element is considered sorted).
  2. Repeatedly merge sublists to produce new sorted sublists until there is only 1 sublist remaining. This will be the sorted list.

Merge Sort Algorithm – Code Visualization

Program on Github

Program

Output

Merge Sort Algorithm - programminginpython.com
Merge Sort Algorithm – programminginpython.com
Merge Sort Algorithm - programminginpython.com
Merge Sort Algorithm – programminginpython.com

Program on Github

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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