Java Array of unique randomly generated integers

Question

public static int[] uniqueRandomElements (int size) {

    int[] a = new int[size];

    for (int i = 0; i < size; i++) {
        a[i] = (int)(Math.random()*10);
         


        

Answer 1

If you just don't want to pay for the added overhead to ArrayList, you can just use an array and use Knuth shuffle:

public Integer[] generateUnsortedIntegerArray(int numElements){
    // Generate an array of integers
    Integer[] randomInts = new Integer[numElements];
    for(int i = 0; i < numElements; ++i){
        randomInts[i] = i;
    }
    // Do the Knuth shuffle
    for(int i = 0; i < numElements; ++i){
        int randomIndex = (int)Math.floor(Math.random() * (i + 1));
        Integer temp = randomInts[i];
        randomInts[i] = randomInts[randomIndex];
        randomInts[randomIndex] = temp;
    }
    return randomInts;
}

The above code produces numElements consecutive integers, without duplication in a uniformly random shuffled order.