Shuffle a deck of cards

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

Asked in Amazon Interview

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++

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// 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;
}

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Java

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// 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

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Python3

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# 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

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C#

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// 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.

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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.

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