Selection Sort Algorithm

Selection sort is a sorting algorithm, specifically an in-place comparison sort.

It has O(n²) time complexity, making it inefficient on large lists, and generally performs worse than the similar insertion sort.

Selection sort is noted for its simplicity, and it has performance advantages over more complicated algorithms in certain situations, particularly where auxiliary memory is limited.

The algorithm divides the input list into two parts: the sublist of items already sorted, which is built up from left to right at the front (left) of the list, and the sublist of items remaining to be sorted that occupy the rest of the list.

Initially, the sorted sublist is empty and the unsorted sublist is the entire input list. The algorithm proceeds by finding the smallest (or largest, depending on sorting order) element in the unsorted sublist, exchanging (swapping) it with the leftmost unsorted element (putting it in sorted order), and moving the sublist boundaries one element to the right.

Performance

Worst-case performance :- O(n²)
Best-case performance :- O(n²)
Average performance :- O(n²)
Worst-case space complexity О(n) total, O(1) auxiliary

Java Program of Selection Sort Algorithm


package com.codenuclear;

public class SelectionSort {
	
	void selectionSort(int[] inputArr){  
        
		int n = inputArr.length;
		for (int i = 0; i < n-1; i++)  
        {  
            int minIndex = i;  
            for (int j = i + 1; j < n; j++){  
                if (inputArr[j] < inputArr[minIndex])
                {  
                	minIndex = j; //Finding lowest index  
                }  
            }  
            
            //Swap the minimum found element with lowest index element
            int temp = inputArr[minIndex];
            inputArr[minIndex] = inputArr[i];
            inputArr[i] = temp;  
        }  
    }  
       
	/* Printing sorted array */
	void printArray(int inputArr[]) {
		int n = inputArr.length;
		for (int i = 0; i < n; ++i)
			System.out.print(inputArr[i] + " ");
		System.out.println();
	}
	
    public static void main(String a[]){  
    	
    	SelectionSort obj = new SelectionSort();
		int inputArr[] = { 20, 3, 35, 11, 2 };
		System.out.println("Input Array before Selection Sort.");
		obj.printArray(inputArr);
		
		obj.selectionSort(inputArr);
		System.out.println("\nSorted Array after Selection Sort.");
		obj.printArray(inputArr);
    }  
}