Stooge Sort

4.1

The Stooge sort is a recursive sorting algorithm. It is defined as below (for ascending order sorting).

Step 1 : If value at index 0 is greater than
         value at last index, swap them.
Step 2:  Recursively,
       a) Stooge sort the initial 2/3rd of the array.
       b) Stooge sort the last 2/3rd of the array.
       c) Stooge sort the initial 2/3rd again to confirm.

NOTE: Always take the ceil of ((2/3)*N) for selecting elements.


Illustration:

Input :   2 4 5 3 1
Output : 1 2 3 4 5
Explanation:
Initially, swap 2 and 1 following above step 1.
          1 4 5 3 2
          Now, recursively sort initial 2/3rd of the elements.
          1 4 5 3 2
          1 3 4 5 2 
          Then, recursively sort last 2/3rd of the elements.
          1 3 4 5 2
          1 2 3 4 5
          Again, sort the initial 2/3rd of the elements to confirm final data is sorted.
          1 2 3 4 5

stooge_sort

C++

// C++ code to implement stooge sort
#include <iostream>
using namespace std;

// Function to implement stooge sort
void stoogesort(int arr[],int l, int h)
{
    if (l >= h)
      return;

    // If first element is smaller than last,
    // swap them
    if (arr[l] > arr[h])
       swap(arr[l], arr[h]);

    // If there are more than 2 elements in
    // the array
    if(h-l+1>2)
    {
        int t = (h-l+1)/3;

        // Recursively sort first 2/3 elements
        stoogesort(arr, l, h-t);

        // Recursively sort last 2/3 elements
        stoogesort(arr, l+t, h);

        // Recursively sort first 2/3 elements
        // again to confirm
        stoogesort(arr, l, h-t);
    }
}

// Driver Code
int main()
{
    int arr[] = {2, 4, 5, 3, 1};
    int n = sizeof(arr)/sizeof(arr[0]);

    // Calling Stooge Sort function to sort
    // the array
    stoogesort(arr, 0, n-1);

    // Display the sorted array
    for (int i=0; i<n; i++)
        cout << arr[i] << " ";

    return 0;
}

Java

// Java program to implement stooge sort
import java.io.*;

public class stooge
{
    // Function to implement stooge sort
    static void stoogesort(int arr[], int l, int h)
    {
        if (l >= h)
           return;

        // If first element is smaller
        // than last,swap them
        if (arr[l] > arr[h])
        {
            int t = arr[l];
            arr[l] = arr[h];
            arr[h] = t;
        }

        // If there are more than 2 elements in
        // the array
        if (h-l+1 > 2)
        {
            int t = (h-l+1) / 3;

            // Recursively sort first 2/3 elements
            stoogesort(arr, l, h-t);

            // Recursively sort last 2/3 elements
            stoogesort(arr, l+t, h);

            // Recursively sort first 2/3 elements
            // again to confirm
            stoogesort(arr, l, h-t);
        }
    }

    // Driver Code
    public static void main(String args[])
    {
        int arr[] = {2, 4, 5, 3, 1};
        int n = arr.length;

        stoogesort(arr, 0, n-1);

        for (int i=0; i < n; i++)
             System.out.print(arr[i] + " ");
    }
}
// Code Contributed by Mohit Gupta_OMG <(0_o)>

Python3

# Python program to implement stooge sort

def stoogesort(arr, l, h):
    if l >= h:
        return
 
    # If first element is smaller
    # than last,swap them
    if arr[l]>arr[h]:
        t = arr[l]
        arr[l] = arr[h]
        arr[h] = t
 
    # If there are more than 2 elements in
    # the array
    if h-l+1 > 2:
        t = (int)((h-l+1)/3)
 
        # Recursively sort first 2/3 elements
        stoogesort(arr, l, (h-t))
 
        # Recursively sort last 2/3 elements
        stoogesort(arr, l+t, (h))
 
        # Recursively sort first 2/3 elements
        # again to confirm
        stoogesort(arr, l, (h-t))
 

# deriver 
arr = [2, 4, 5, 3, 1]
n = len(arr)

stoogesort(arr, 0, n-1)
 
for i in range(0, n):
    print(arr[i], end = ' ')

# Code Contributed by Mohit Gupta_OMG <(0_o)>


Output:

1 2 3 4 5 

The running time complexity of stooge sort can be written as,

T(n) = 3T(3n/2) + Θ(1)

Solution of above recurrence is O(n(log3/log1.5)) = O(n2.709), hence it is slower than even bubble sort(n^2).

Reference:
Wikipedia

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

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