Agfdhyk

I know there is an efficient shuffling algorithm called Fisher Yates I believe but I try to build a custom one (out of stubbornness).

I am trying to generate a new random number in the right range, than use it to determine a new random place in a copied array. And then store this random number to NOT use it twice.
My method does not work. Would someone care to give me some enlightment?

public int shuffled(int numbers) {

    int rand;

    int copyNumbers = new int[numbers.length];

    int usedRand = new int[numbers.length];





    for (int i = 0; i < numbers.length; i++) {

        rand = new Random().nextInt(numbers.length + 1);

        if ((i != rand) && (usedRand[i]!=rand)) {

            copyNumbers[rand] = numbers[i];

            usedRand[i]=rand;

        }

    }

    numbers = copyNumbers;

    return numbers;

}

As I already pointed the errors out in the comments. Here is possible implementation of shuffle(). I commented the code based on my modifications.
If you happen to have questions, please feel free to ask!

public static void main(String args) {

    //sample values

    int numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18};



    //First call of recursive function

    int x = shuffled(numbers, null, null, false, 0);



    //Print out values

    for (int i = 0; i < x.length; i++) {

        System.out.print(x[i] + "|");

    }

}



public static int shuffled(int numbers, int usedRand, int copyNumbers, boolean newRandomValue, int current) {



    //Initialisation

    int rand = -1;

    int start = 0;



    //If function hasn't been called before, initialise.

    if (usedRand == null) {

        usedRand = new int[numbers.length];

        Arrays.fill(usedRand, -1);

    }

    if (copyNumbers == null) {

        copyNumbers = new int[numbers.length];

    }



    //If function has been called recursively, reassign the start-Integer for for-loop

    if (newRandomValue) {

        start = current;

    }



    //Iterate over numbers-array with <start> as start-index

    for (int i = start; i < numbers.length; i++) {

        /*

            new Random().nextInt(numbers.length+1 ) gets a random number between 0 and numbers.length + 1

            In our example, numbers.length+1 is 20. So we will get a random number between 0 and 20. 

            But we want to get random values between -1 and 19, so 

            new Random().nextInt(numbers.length+1 ) --> values between 0 to 20

            rand = new Random().nextInt(numbers.length+1 ) -1  --> values between -1 to 19

         */

        rand = new Random().nextInt(numbers.length+1 ) -1;



        //Iterate through usedRand array and compare if current rand value has already been used yet.

        for (int j = 0; j < usedRand.length; j++) {

            if (usedRand[j] == rand) {

                /*

                    If current rand value has already been used, recursively call shuffle again with the current index i

                    as new start-index

                 */

                return shuffled(numbers, usedRand, copyNumbers, true, i);

            }

        }

        copyNumbers[rand] = numbers[i];

        usedRand[i] = rand;

    }

    numbers = copyNumbers;

    return numbers;

}