BogoSort or Permutation Sort

2.4

BogoSort also known as permutation sort, stupid sort, slow sort, shotgun sort or monkey sort is a particularly ineffective algorithm based on generate and test paradigm. The algorithm successively generates permutations of its input until it finds one that is sorted.(Wiki)
For example, if bogosort is used to sort a deck of cards, it would consist of checking if the deck were in order, and if it were not, one would throw the deck into the air, pick the cards up at random, and repeat the process until the deck is sorted.

PseudoCode:

while not Sorted(list) do
    shuffle (list)
done


Example:

Let us consider an example array ( 3 2 5 1 0 4 )
4 5 0 3 2 1 (1st shuffling)
4 1 3 2 5 0 (2ndshuffling)
1 0 3 2 5 4 (3rd shuffling)
3 1 0 2 4 5 (4th shuffling)
1 4 5 0 3 2 (5th shuffling)
.
.
.
0 1 2 3 4 5 (nth shuffling)—— Sorted Array

Here, n is unknown because algorithm doesn’t known in which step the resultant permutation will come out to be sorted.

C++

// C++ implementation of Bogo Sort
#include<bits/stdc++.h>
using namespace std;

// To check if array is sorted or not
bool isSorted(int a[], int n)
{
    while ( --n > 1 )
        if (a[n] < a[n-1])
            return false;
    return true;
}

// To generate permuatation of the array
void shuffle(int a[], int n)
{
    for (int i=0; i < n; i++)
        swap(a[i], a[rand()%n]);
}

// Sorts array a[0..n-1] using Bogo sort
void bogosort(int a[], int n)
{
    // if array is not sorted then shuffle
    // the array again
    while ( !isSorted(a, n) )
        shuffle(a, n);
}

// prints the array
void printArray(int a[], int n)
{
    for (int i=0; i<n; i++)
        printf("%d ", a[i]);
    printf("\n");
}

// Driver code
int main()
{
    int a[] = {3, 2, 5, 1, 0, 4};
    int n = sizeof a/sizeof a[0];
    bogosort(a, n);
    printf("Sorted array :\n");
    printArray(a,n);
    return 0;
}

Java

// Java Program to implement BogoSort
public class BogoSort
{
    // Sorts array a[0..n-1] using Bogo sort
    void bogoSort(int[] a)
    {
        // if array is not sorted then shuffle the
        // array again
        while (isSorted(a) == false)
            shuffle(a);
    }

    // To generate permuatation of the array
    void shuffle(int[] a)
    {
         // Math.random() returns a double positive
         // value, greater than or equal to 0.0 and
         // less than 1.0.
         for (int i=1; i <= n; i++)
             swap(a, i, (int)(Math.random()*i));
    }

    // Swapping 2 elements
    void swap(int[] a, int i, int j)
    {
        int temp = a[i];
        a[i] = a[j];
        a[j] = temp;
    }

    // To check if array is sorted or not
    boolean isSorted(int[] a)
    {
        for (int i=1; i<a.length; i++)
            if (a[i] < a[i-1])
                return false;
        return true;
    }

    // Prints the array
    void printArray(int[] arr)
    {
        for (int i=0; i<arr.length; i++)
            System.out.print(arr[i] + " ");
        System.out.println();
    }

    public static void main(String[] args)
    {
        //Enter array to be sorted here
        int[] a = {3, 2, 5, 1, 0, 4};
        BogoSort ob = new BogoSort();

        ob.bogoSort(a);

        System.out.print("Sorted array: ");
        ob.printArray(a);
    }
}

Python

# Python program for implementation of Bogo Sort
import random

# Sorts array a[0..n-1] using Bogo sort
def bogoSort(a):
    n = len(a)
    while (is_sorted(a)== False):
        shuffle(a)

# To check if array is sorted or not
def is_sorted(a):
    n = len(a)
    for i in range(0, n-1):
        if (a[i] > a[i+1] ):
            return False
    return True

# To generate permuatation of the array
def shuffle(a):
    n = len(a)
    for i in range (0,n):
        r = random.randint(0,n-1)
        a[i], a[r] = a[r], a[i]

# Driver code to test above
a = [3, 2, 4, 1, 0, 5]
bogoSort(a)
print("Sorted array :")
for i in range(len(a)):
    print ("%d" %a[i]),

Output:

Sorted array :
0 1 2 3 4 5 

Time Complexity:

  • Worst Case : O(∞) (since this algorithm has no upper bound)
  • Average Case: O(n*n!)
  • Best Case : O(n)(when array given is already sorted)

Auxiliary Space : O(1)

This article is contributed by Rahul Agrawal . 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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