Python Program for Gnome Sort

Gnome Sort is a simple comparison-based algorithm similar to Insertion Sort. It repeatedly swaps adjacent elements if they are out of order and moves backward until all elements are correctly placed.

Algorithm Steps:

1. Start from the first element (index 0).
2. If at the start of the array, move one step forward.
3. If the current element is greater than or equal to the previous element, move one step forward.
4. If the current element is smaller than the previous element, swap both elements and move one step backward.
5. Repeat steps 2-4 until the end of the array is reached.

Illustration of Gnome Sort

Let’s take an example: Input: [5, 3, 2, 4]

1. Compare 5 and 3, out of order, swap -> [3, 5, 2, 4], move one step back.
2. At start, move forward.
3. Compare 5 and 2, out of order, swap -> [3, 2, 5, 4], move one step back.
4. Compare 3 and 2, out of order, swap -> [2, 3, 5, 4], move one step back.
5. At start, move forward.
6. Compare 2 and 3, in order, move forward.
7. Compare 3 and 5, in order, move forward.
8. Compare 5 and 4, out of order, swap -> [2, 3, 4, 5], move one step back.
9. Compare 3 and 4, in order, move forward.

Final sorted list: [2, 3, 4, 5]

Code Implementation:

def gnomeSort(arr, n):
    ind = 0
    while ind < n:
        if ind == 0:
            ind += 1
        if arr[ind] >= arr[ind - 1]:
            ind += 1
        else:
            arr[ind], arr[ind - 1] = arr[ind - 1], arr[ind]
            ind -= 1
    return arr

arr = [34, 2, 10, -9]
n = len(arr)

arr = gnomeSort(arr, n)
print( *arr)

-9 2 10 34

Explanation:

• ind = 0: Initialize the starting position at the first element.
• while ind < n: Continue the loop until the entire list is traversed.
• if ind == 0: If we are at the start, move one step forward since there’s nothing to compare.
• if arr[ind] >= arr[ind- 1]: If the current element is in correct order with the previous one, move forward.
• else: If the elements are out of order, swap them.
• arr[index], arr[index - 1] = arr[index - 1], arr[index]: Swap adjacent elements that are not in order.
• index -= 1: After swapping, move one step back to recheck the order.
• return arr: Once all elements are in the correct order, return the sorted list.

Related Articles:

• Insertion Sort - Python
• Bubble Sort - Python