Gnome Sort also called Stupid sort is based on the concept of a Garden Gnome sorting his flower pots. A garden gnome sorts the flower pots by the following method-

- He looks at the flower pot next to him and the previous one; if they are in the right order he steps one pot forward, otherwise he swaps them and steps one pot backwards.
- If there is no previous pot (he is at the starting of the pot line), he steps forwards; if there is no pot next to him (he is at the end of the pot line), he is done.

**Input** –

Array- arr[] Total elements - n

**Algorithm Steps**

- If you are at the start of the array then go to the right element (from arr[0] to arr[1]).
- 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++;

- 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--; }

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

Example-

34 2 10 -9

**Underlined elements**are the pair under consideration.**“Red” colored**are the pair which needs to be swapped.- Result of the swapping is colored as
**“blue”**

Below is C++ implementation of the algorithm.

## C++

// A C++ Program to implement Gnome Sort #include<iostream> using namespace std; // A function to sort the algorithm using gnome sort void gnomeSort(int arr[], int n) { int index = 0; while (index < n) { if (index == 0) index++; if (arr[index] >= arr[index-1]) index++; else { swap(arr[index], arr[index-1]); index--; } } return; } // A utility function ot print an array of size n void printArray(int arr[], int n) { cout << "Sorted sequence after Gnome sort: "; for (int i=0; i < n; i++) cout << arr[i] << " "; cout << "\n"; } // Driver program to test above functions. int main() { int arr[] = {34, 2, 10, -9}; int n = sizeof(arr)/sizeof(arr[0]); gnomeSort(arr, n); printArray(arr, n); return (0); }

## 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

## Python

# Python program to implement Gnome Sort # A function to sort the given list using Gnome sort def gnomeSort( arr, n): index = 0 while index < n: if index == 0: index = index + 1 if arr[index] >= arr[index - 1]: index = index + 1 else: arr[index], arr[index-1] = arr[index-1], arr[index] index = index - 1 return arr # Driver Code arr = [ 34, 2, 10, -9] n = len(arr) arr = gnomeSort(arr, n) print "Sorted seqquence after applying Gnome Sort :", for i in arr: print i, # Contributed By Harshit Agrawal

Output:

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

**Time Complexity** – As there are 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). This is because the variable – ‘index’ in our program doesn’t always gets incremented, it gets decremented too.

*However this sorting algorithm is adaptive and performs better if the array is already/partially sorted.*

**Auxiliary Space** – This is an in-place algorithm. So O(1) auxiliary space is needed.

This article is contributed by **Rachit Belwariar**. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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