Java Program for Gnome Sort

Algorithm Steps

1. If you are at the start of the array then go to the right element (from arr[0] to arr[1]).
2. If the current array element is larger or equal to the previous array element then go one step right

                   if (arr[i] >= arr[i-1])
                      i++;

1. If the current array element is smaller than the previous array element then swap these two elements and go one step backwards

                       if (arr[i] < arr[i-1])
                       {
                           swap(arr[i], arr[i-1]);
                           i--;
                       }

1. Repeat steps 2) and 3) till ‘i’ reaches the end of the array (i.e- ‘n-1’)
2. If the end of the array is reached then stop and the array is sorted.

Java

// Java Program to implement Gnome Sort

import java.util.Arrays;
public class GFG {
 static void gnomeSort(int arr[], int n)
 {
  int index = 0;

  while (index < n) {
   if (index == 0)
    index++;
   if (arr[index] >= arr[index - 1])
    index++;
   else {
    int temp = 0;
    temp = arr[index];
    arr[index] = arr[index - 1];
    arr[index - 1] = temp;
    index--;
   }
  }
  return;
 }

 // Driver program to test above functions.
 public static void main(String[] args)
 {
  int arr[] = { 34, 2, 10, -9 };

  gnomeSort(arr, arr.length);

  System.out.print("Sorted sequence after applying Gnome sort: ");
  System.out.println(Arrays.toString(arr));
 }
}

// Code Contributed by Mohit Gupta_OMG

Output:

Sorted sequence after applying Gnome sort: [-9, 2, 10, 34]

Time Complexity: O(n²). As there is no nested loop (only one while) it may seem that this is a linear O(n) time algorithm. But the time complexity is O(n^2) as the variable ‘index’ in the program doesn’t always get incremented, it gets decremented too. 
Auxiliary Space: O(n)

For understanding of Arrays.toString(), Please refer : https://www.geeksforgeeks.org/arrays-tostring-in-java-with-examples/ Please refer complete article on Gnome Sort for more details!