In this article, we will be discussing everything about Selection sort - Selection sort algorithm, Selection sort program in C, C++, Java, Selection sort time complexity etc.
Prerequisite: Bubble Sort Algorithm
A Selection sort algorithm sorts an array of elements by iterating and finding the smallest/largest one and then putting it aside into a sorted list. It continues to sort by finding the smallest/largest unsorted element and adding it to the sorted list of elements.This happens until there are no elements left in the unsorted list.
Assume that the array A = [14,16, 3, 6, 50]needs to be sorted in ascending order.
So now, the minimum element in the array i.e.3 is searched for and then swapped with the element that is currently located in the first position, i.e.14. Now the minimum element in the remaining unsorted array is searched for and put in the second position, and so on. Have a look at the implementation explained below.
for i = 0 to n - 1 // Finding the minimum element in unsorted array min = i for j = i + 1 to n if arr[j] < arr[min] then min = j end if end for // Swapping the found minimum element with the first element swap(arr[min], arr[i]) end for
Here is the implementation of selection sort in various languages.
To find the smallest element from the array of n elements, n?1 comparisons are required. After putting the smallest element in the sorted array list, the size of an unsorted array reduces to n?1 and then n?2 comparisons are required to find the next minimum in the unsorted array.
(N?1)+(N?2)+.......+1=(N?(N?1))/2 comparisons and N swaps result in the overall complexity of O(N2).
|Efficiency||Improved efficiency as compared to bubble sort|
Inefficient due to a large number of comparisons to be made in each iteration
|Best case time complexity||O(N2). In Selection sort, we cannot identify if the array is sorted or not within the 1st iteration.|
O(n). In Bubble sort, we can identify whether a list is sorted within the 1st iteration.