Question

Write a simple Java program that that sorts the following array, 5 7 4 9 8 5 6 3, using a selection sort algorithm. What is the Big O of the algorithm?

Answer 1

public class Selection_sort {
    private static void swap(int[] array, int i, int j) {
        int temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }

    public static void selectionSort(int[] array) {
        for (int i = 0; i < array.length - 1; i++) {
            int lowindex = i;
            for (int j = array.length - 1; j > i; j--)
                if (array[j] < (array[lowindex])) {
                    lowindex = j;
                }
            swap(array, i, lowindex);
        }
    }

    public static void main(String[] args) {
        int arr[] = {5, 7, 4, 9, 8, 5, 6, 3};
        selectionSort(arr);
        for(int i = 0;i<arr.length;i++){
            System.out.print(arr[i]+" ");
        }
        System.out.println();
    }
}

3 4 5 5 6 7 8 9 

First for loop is running for i values from 0 to n with an increment of 1
So, it runs for O(n) times
Inner for loop is running for j values from n to i with a decrement of 1
So, At max it runs max of O(n) times
So, total time complexity = O(n*n) = 

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