# Gnome Sort

• Difficulty Level : Basic
• Last Updated : 14 Jun, 2022

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

### How gnome sort works?

Lets consider an example: arr[] = {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” Algorithm Steps:

• If you are at the start of the array then go to the right element (from arr to arr).
• 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.

Below is the implementation of the algorithm.

## C++

 `// A C++ Program to implement Gnome Sort``#include ``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);`` ` `    ``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 sequence after applying Gnome Sort :"``,``for` `i ``in` `arr:``    ``print` `i,`` ` `# Contributed By Harshit Agrawal`

## C#

 `// C# Program to implement Gnome Sort``using` `System;`` ` `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()``    ``{``        ``int``[] arr = { 34, 2, 10, -9 };``         ` `        ``// Function calling``        ``gnomeSort(arr, arr.Length);`` ` `        ``Console.Write(``"Sorted sequence after applying Gnome sort: "``);`` ` `        ``for` `(``int` `i = 0; i < arr.Length; i++)``            ``Console.Write(arr[i] + ``" "``);``    ``}``}`` ` `// This code is contributed by Sam007`

## PHP

 `= ``\$arr``[``\$index` `- 1])``            ``\$index``++;``        ``else` `        ``{``            ``\$temp` `= 0;``            ``\$temp` `= ``\$arr``[``\$index``];``            ``\$arr``[``\$index``] = ``\$arr``[``\$index` `- 1];``            ``\$arr``[``\$index` `- 1] = ``\$temp``;``            ``\$index``--;``        ``}``    ``}``    ``echo` `"Sorted sequence "``, ``         ``"after Gnome sort: "``;``    ``for` `(``\$i` `= 0; ``\$i` `< ``\$n``; ``\$i``++)``        ``echo` `\$arr``[``\$i``] . ``" "``;``    ``echo` `"\n"``; ``}`` ` `// Driver Code``\$arr` `= ``array``(34, 2, 10, -9);``\$n` `= ``count``(``\$arr``);`` ` `gnomeSort(``\$arr``, ``\$n``);`` ` `// This code is contributed``// by Sam007``?>`

## Javascript

 ``

Output

`Sorted sequence after 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.

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