C++ Program to Implement Fisher-Yates Algorithm for Array Shuffling

Shuffling an array means rearranging its elements in a random order. The Fisher-Yates algorithm creates a shuffle where every possible order is equally likely to happen. In this article, we'll show you how to write a C++ program that uses Fisher-Yates algorithm to shuffle an array.

Fisher-Yates Algorithm to Shuffle an Array

To shuffle an array, we use the Fisher-Yates algorithm. It works by swapping each element with another randomly selected element from the part of the array that we haven't shuffled yet.

Here are the steps we follow:

• First, we start with the last element of the array.
• Second, we pick a random index from the start of the array up to the current element's position.
• Next, we swap the current element with the element at the random index.
• Then, we move one step backward and repeat the process.
• Finally, we continue until we reach the first element, completing the shuffle.

C++ Program to Shuffle an Array Using Fisher-Yates Algorithm

Below is a C++ program where we use the Fisher-Yates algorithm to shuffle the elements of an array in random order. This method is fair because each item has an equal chance to appear in any position.

#include <iostream>
#include <cstdlib>  
#include <ctime>    

using namespace std;

// Function to perform Fisher-Yates shuffle on array arr of size n
void fisherYatesShuffle(int arr[], int n) {
    srand(time(0));

    // Start from the last element and swap with a random element before it (including itself)
    for (int i = n - 1; i > 0; i--) {
        // Generate a random index between 0 and i
        int j = rand() % (i + 1);

        // Swap arr[i] with arr[j]
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
}

int main() {
    int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
    int n = sizeof(arr) / sizeof(arr[0]);
    cout << "Original array: ";
    for (int i = 0; i < n; i++) {
        cout << arr[i] << " ";
    }
    cout << endl;
    // Shuffle the array
    fisherYatesShuffle(arr, n);
    cout << "Shuffled array: ";
    for (int i = 0; i < n; i++) {
        cout << arr[i] << " ";
    }
    return 0;
}

The output below shows the original array and the shuffled array using the Fisher-Yates algorithm.

Original array: 1 2 3 4 5 6 7 8 9 
Shuffled array: 3 4 6 7 8 1 9 2 5