# C++ Program for Gnome Sort

• Last Updated : 13 Jun, 2022

Algorithm Steps

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

## CPP

 `// 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); ` `} `

Output:

`Sorted sequence after 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(1)

Please refer complete article on Gnome Sort for more details!

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