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-
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”
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// A C Program to implement Gnome Sort#include<stdio.h>
// A function to swap the array elements
// at the index - 'i' and 'j'
void swap(int arr[], int i, int j)
{
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
return;
}
// A utility function ot print an array of size n
void printArray(int arr[], int n)
{
int i;
printf("Sorted sequence after applying Gnome sort: ");
for (i=0; i < n; i++)
printf("%d ", arr[i]);
printf("\n");
}
// 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, index-1);
index--;
}
}
return;
}
// 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);
}
Output:
Sorted sequence after applying Gnome sort: -9 2 10 34Time 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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