Stooge Sort

14 Jun, 2022
Stooge Sort is a recursive sorting algorithm. It is not much efficient but interesting sorting algorithm. It generally divides the array into two overlapping parts (2/3 each). After that it performs sorting in first 2/3 part and then it performs sorting in last 2/3 part. And then, sorting is done on first 2/3 part to ensure that the array is sorted.
The key idea is that sorting the overlapping part twice exchanges the elements between the other two sections accordingly.
Approach:
Step 1: If value at index 0 is greater than value at last index, swap them.Step 2: Recursively, 
Stooge sort the initial 2/3rd of the array.
Stooge sort the last 2/3rd of the array.
Stooge sort the initial 2/3rd again to confirm.
NOTE: Always take the ceil of ((2/3)*N) for selecting elements.  
Illustration:  
Lets consider an example: arr[] = {2, 4, 5, 3, 1}
Step1: Initially, First and last elements are compared and if last is greater than first then they are swapped.
Step2: Now, recursively sort initial 2/3rd of the elements as shown below:
Step3: Then, recursively sort last 2/3rd of the elements, as shown below:
Step4: Again, sort the initial 2/3rd of the elements to confirm final data is sorted.Resulted array:
Resulted array:
Below is the implementation for the above approach:
C++
Java
Python3
C#
Javascript
// C++ code to implement stooge sort#include <iostream>using namespace std;  // Function to implement stooge sortvoid 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 Codeint 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 program to implement stooge sortimport 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)>
# 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)>
// C# program to implement stooge sortusing System;  class GFG {          // 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()    {        int[] arr = { 2, 4, 5, 3, 1 };        int n = arr.Length;          // Calling Stooge Sort function        // to sort the array        stoogesort(arr, 0, n - 1);          // Display the sorted array        for (int i = 0; i < n; i++)            Console.Write(arr[i] + " ");    }}  // This code is contributed by Sam007.
<script>    // Javascript program to implement stooge sort          // Function to implement stooge sort    function stoogesort(arr, l, h)    {        if (l >= h)            return;            // If first element is smaller        // than last, swap them        if (arr[l] > arr[h]) {            let 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) {            let t = parseInt((h - l + 1) / 3, 10);                // 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);        }    }          let arr = [ 2, 4, 5, 3, 1 ];    let n = arr.length;      // Calling Stooge Sort function    // to sort the array    stoogesort(arr, 0, n - 1);      // Display the sorted array    for (let i = 0; i < n; i++)      document.write(arr[i] + " ");      </script>
1 2 3 4 5 
The running time complexity of stooge sort can be written as,T(n) = 3T(3n/2) + ?(1)
Solution of above recurrence is O(n(log3/log1.5)) = O(n2.709), hence it is slower than even bubble sort(n^2).
This article is contributed by DANISH KALEEM. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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