write a program to sort a list using selection sort in python

 

Selection Sort in Python

In this tutorial, we will implement the selection sort algorithm in Python. It is quite straightforward algorithm using the less swapping.

In this algorithm, we select the smallest element from an unsorted array in each pass and swap with the beginning of the unsorted array. This process will continue until all the elements are placed at right place. It is simple and an in-place comparison sorting algorithm.

Code -

1. def selection_sort(array):  
2.     length = len(array)  
3.       
4.     for i in range(length-1):  
5.         minIndex = i  
6.           
7.         for j in range(i+1, length):  
8.             if array[j]<array[minIndex]:  
9.                 minIndex = j  
10.                   
11.         array[i], array[minIndex] = array[minIndex], array[i]  
12.           
13.           
14.     return array      
15. array = [21,6,9,33,3]  
16.   
17. print("The sorted array is: ", selection_sort(array))  

Output:

The sorted array is:  [3, 6, 9, 21, 33]

Explanation -

Let's understand the above code -

• First, we define the selection_sort() function that takes array as an argument.
• In the function, we get the length of the array which used to determine the number of passes to be made comparing values.
• As we can see that, we use two loops - outer and inner loop. The outer loop uses to iterate through the values of the list. This loop will iterate to 0 to (length-1). So the first iteration will be perform (5-1) or 4 times. In each iteration, the value of the variable i is assigned to the variable
• The inner loop uses to compare the each value of right-side element to the other value on the leftmost element. So the second loop starts its iteration from i+1. It will only pick the value that is unsorted.
• Find the minimum element in the unsorted list and update the minIndex position.
• Place the value at the beginning of the array.
• Once the iteration is completed, the sorted array is returned.
• At last we create an unsorted array and pass to the selection_sort() It prints the sorted array.