shuffle a 3d array in c++

Question

I have this piece of code which creates a 3d array and places 1-9 in a 3x3x3 box. I need to find a way to shuffle the elements of this array to compare how closely the newly shuffled array is to a magic square. Any ideas are appreciated! Thanks!

 for(i = 0; i < x; i++)
{
    cout << "Finding a Magic Square..." << endl;

    for(j = 0; j < y; j++)
    {
        cout << endl;

        for(k = 0; k < z; k++)
        {
            array3D[i][j][k] = (i+1) + (j * z) + k;
            cout << '\t' << array3D[i][j][k];
        }
    }

    cout << endl << endl;
}

Answer 1

You can use std::random_shuffle(...) but you have to use it properly to have truly random permutations. Iteratively using random_shuffle on a 2D array will yield in related entries per row.

#include <algorithm>
#include <iterator>
#include <iostream>
#include <cstdlib>
#include <ctime>

int main () {
    std::srand(std::time(NULL)); // initialize random seed

    // shuffle a 2D array
    int arr[3][3] = {
        {0, 1, 2},
        {3, 4, 5},
        {6, 7, 8}
    };

    // Shuffle from the first member to the last member.
    // The array is interpreted as a 9 element 1D array.
    std::random_shuffle(&arr[0][0], &arr[2][3]);

    // print the result
    for (int row = 0; row < 3; ++row) {
        for (int col = 0; col < 3; ++col) {
            std::cout << arr[row][col] << ' ';
        }
        std::cout << std::endl;
    }
    return 0;
}

Online demo: http://ideone.com/C4PlRs

Answer 2

you can use std::random_shuffle to shuffle the array.