random numbers into an array

[geisteskrankhei]

Basically, I have to make a code that requests user input. The program asks them to tell me how many columns/rows the user wants the magic square to have. I need to then generate random numbers for each spot.

ex: user inputs 3, out put looks like

3 7 1
6 4 9
8 2 5

I know how to generate a single random number but I've been trying to figure out how I'm going to get as many as the user needs.

Numbers cannot be duplicated, but I can tackle that if statement on my own easily. it's just the part that involves multiple random numbers put into an array that I am having difficulty on. Any help would be greatly appreciated. So far, my code looks like:

import java.awt.*;
import hsa.Console;
import java.util.Random;

public class MagicSquare
{
    static Console c;           

    public static void main (String[] args)
    {
        c = new Console ();

        Random random = new Random ();
        c.println ("How many numbers up/down and left/right would you like in your magic square?");
        int size = c.readInt ();
        int NumberOfRandoms = (size * size);
        int myRandomNumber = random.nextInt (NumberOfRandoms) + 1;
        c.println (myRandomNumber);

        
    } 
}

[javaAddict]

Since the user inputs the size you can create the array:

int [][] array=new int[N][N];

Then use a for-loop to put numbers in the array.

As I noticed at your example the random numbers are from 1 to 9. Is that a requirement? Meaning do the numbers have to be from 1 to N*N?

[geisteskrankhei]

Yes, it must be from 1 to N*N, with no numbers repeating. To make it easier I was thinking about making a for loop to generate numbers from 1 to N*N, not randomly. But, put them into the array and then shuffle them. I am having trouble generating randoms and putting them into a for loop. I have:

int [] [] Randoms = new int [size] [size];
        for (int row = 0 ; row < Randoms.length ; row++)
            for (int col = 0 ; col < Randoms [0].length ; col++)
                Randoms [row] [col] = myRandomNumber;

[Ezzaral]

You're on the right track generating the list of numbers 1 to N*N into an array and then shuffling them. You just need to consider how to pick a random place in the array to place each number.

[javaAddict]

One suggestion is this:
you could have an array with values from 1 to N*N like this: (example)
int [] oneDim= {1,2,3,4,5,6,7,8,9};

Generate a random number from 0 to 8.
Take that number and put it inside the 2-sized array.Use a for loop that puts the first taken number to (0,0).
Then use a swap method that takes the selected number and puts it at the end of the 1-sized array:
example: if the random number was 4, Then the oneDim[4]=5 will be put at the target 2-sized array, and after the swap the oneDim will be like this: {1,2,3,4,9,6,7,8,5}

Then you will repeat the above procedure with one difference: the random generated number will be from 0 to 7. So when you go to the oneDim array you will take only the first 8 numbers: {1,2,3,4,9,6,7,8} and you will not take the last which is already used: 5

int [] oneDim= new int[N]
int [][] randoms=[N][N];

for (int i=0;i<N;i++) {
  oneDim[i]=i+1;
}

int row=0;
int col=0;

for (int i=0;i<N;i++) {
  int r = //random number from 0 to N-1

  //put the value from oneDim to randoms
  randoms[row][col] = oneDim[r];

  //swap oneDim[r]  with oneDim[N-1 - i]  //N-1 - i : so not to keep swapping a number that was previously used and was put at the end 

  //alter row, col so as to put the next number at a new place
}

[Ezzaral]

You really don't even need to have a 2D array. The single 1D array is fine for a uniform rectangular grid, with rows being nothing more than an offset into the array.

I hesitate to say any more though since it's a homework situation.