Stooge Sort - GeeksforGeeks

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.

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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

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)> 

C#

// C# program to implement stooge sort 
using 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. 

Output:

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(n^2.709), hence it is slower than even bubble sort(n^2).

Reference:
Wikipedia

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