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Shuffle a deck of cards

  • Difficulty Level : Easy
  • Last Updated : 17 Apr, 2019

Given a deck of cards, the task is to shuffle them.

Asked in Amazon Interview

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Prerequisite : Shuffle a given array



Algorithm:

1. First, fill the array with the values in order.
2. Go through the array and exchange each element 
   with the randomly chosen element in the range 
   from itself to the end.

// It is possible that an element will be swap
// with itself, but there is no problem with that. 

C++




// C++ program for shuffling desk of cards.
#include <bits/stdc++.h>
using namespace std;
  
// Function which shuffle and print the array
void shuffle(int card[], int n)
{
    // Initialize seed randomly
    srand(time(0));
  
    for (int i=0; i<n ;i++)
    {
        // Random for remaining positions.
        int r = i + (rand() % (52 -i));
  
        swap(card[i], card[r]);
    }
}
  
// Driver code
int main()
{
    // Array from 0 to 51
    int a[] = {0, 1, 2, 3, 4, 5, 6, 7, 8,
               9, 10, 11, 12, 13, 14, 15,
               16, 17, 18, 19, 20, 21, 22,
               23, 24, 25, 26, 27, 28, 29,
               30, 31, 32, 33, 34, 35, 36,
               37, 38, 39, 40, 41, 42, 43,
               44, 45, 46, 47, 48, 49, 50,
               51};
  
    shuffle(a, 52);
  
    // Printing all shuffled elements of cards
    for (int i=0; i<52; i++)
        cout << a[i] << " ";
    cout << endl;
  
    return 0;
}

Java




// Java Code for Shuffle a deck of cards
import java.util.Random;
  
class GFG {
      
    // Function which shuffle and print the array
    public static void shuffle(int card[], int n)
    {
          
        Random rand = new Random();
          
        for (int i = 0; i < n; i++)
        {
            // Random for remaining positions.
            int r = i + rand.nextInt(52 - i);
              
             //swapping the elements
             int temp = card[r];
             card[r] = card[i];
             card[i] = temp;
               
        }
    }
       
    // Driver code
    public static void main(String[] args) 
    {
        // Array from 0 to 51
        int a[] = {0, 1, 2, 3, 4, 5, 6, 7, 8,
                   9, 10, 11, 12, 13, 14, 15,
                   16, 17, 18, 19, 20, 21, 22,
                   23, 24, 25, 26, 27, 28, 29,
                   30, 31, 32, 33, 34, 35, 36,
                   37, 38, 39, 40, 41, 42, 43,
                   44, 45, 46, 47, 48, 49, 50
                   51};
       
        shuffle(a, 52);
       
        // Printing all shuffled elements of cards
        for (int i = 0; i < 52; i ++)
           System.out.print(a[i]+" ");
          
    }
}
// This code is contributed by Arnav Kr. Mandal

Python3




# Python3 program for shuffling desk of cards
# Function which shuffle and print the array 
  
import random
def shuffle(card,n) :
      
    # Initialize seed randomly
    for i in range(n):
          
        # Random for remaining positions.
        r = i + (random.randint(0,55) % (52 -i))
        tmp=card[i]
        card[i]=card[r]
        card[r]=tmp
#Driver code
if __name__=='__main__':
    a=[0, 1, 2, 3, 4, 5, 6, 7, 8,
       9, 10, 11, 12, 13, 14, 15,
       16, 17, 18, 19, 20, 21, 22
       23, 24, 25, 26, 27, 28, 29,
       30, 31, 32, 33, 34, 35, 36,
       37, 38, 39, 40, 41, 42, 43
       44, 45, 46, 47, 48, 49, 50,
       51]
    shuffle(a,52)
    print(a)
         
#this code is contributed by sahilshelangia

C#




// C# Code for Shuffle a deck of cards
using System;
  
class GFG {
      
    // Function which shuffle and 
    // print the array
    public static void shuffle(int []card, 
                               int n)
    {
          
        Random rand = new Random();
          
        for (int i = 0; i < n; i++)
        {
              
            // Random for remaining positions.
            int r = i + rand.Next(52 - i);
              
            //swapping the elements
            int temp = card[r];
            card[r] = card[i];
            card[i] = temp;
              
        }
    }
      
    // Driver code
    public static void Main() 
    {
        // Array from 0 to 51
        int []a = {0, 1, 2, 3, 4, 5, 6, 7, 8,
                   9, 10, 11, 12, 13, 14, 15,
                   16, 17, 18, 19, 20, 21, 22,
                   23, 24, 25, 26, 27, 28, 29,
                   30, 31, 32, 33, 34, 35, 36,
                   37, 38, 39, 40, 41, 42, 43,
                   44, 45, 46, 47, 48, 49, 50, 
                   51};
      
        shuffle(a, 52);
      
        // Printing all shuffled elements of cards
        for (int i = 0; i < 52; i ++)
        Console.Write(a[i]+" ");
          
    }
}
  
// This code is contributed by Nitin Mittal.


Output:
29 27 20 23 26 21 35 51 15 18 46 32 33 19 
24 30 3 45 40 34 16 11 36 50 17 10 7 5 4 
39 6 47 38 28 13 44 49 1 8 42 43 48 0 12 
37 41 25 2 31 14 22

Note : Output will be different each time because of the random function used in the program.
Please refer Shuffle a given array for details.

This article is contributed by Sahil Rajput. 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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