android - generate random numbers with no repeat [duplicate]

Question

can anyone please tell me how to generate random numbers with no repeat example

random (10) should(may) return 3,4,2,1,7,6,5,8,9,10 with no repeat

Thanks

Answer 1

I would suggest adding the numbers to an ArrayList<Integer> and then use Collections.shuffle() to randomize their order. Something like this:

ArrayList<Integer> number = new ArrayList<Integer>();
for (int i = 1; i <= 10; ++i) number.add(i);
Collections.shuffle(number);

Answer 2

Make a list of generated numbers, when your newly generated number is already in this list you make a new random number.

Random rng = new Random(); // Ideally just create one instance globally
List<Integer> generated = new ArrayList<Integer>();
for (int i = 0; i < numbersNeeded; i++)
{
    while(true)
    {
        Integer next = rng.nextInt(max) + 1;
        if (!generated.contains(next))
        {
            // Done for this iteration
            generated.add(next);
            break;
        }
    }
}