Java - how to create a random number from an array of values

Question

on the first iteration- I want to create a random number from 0..10

This is how I've implement it-

 int generator= (int)(Math.random() * (10));

On the first iteration I want to create another random number, but without one of the values. For example I would like the random number without the number 4. only 1,2,3,5,6,7,8,9,0

How can I remove one of the values from the numbers 0..10 when I generate a random number?

Answer 1

1st Way: -

You can also maintain a List of all the numbers. Then use Collections.shuffle to shuffle the list and get the first element. And remove it.

    List<Integer> list = new ArrayList<Integer>();

    list.add(1); 
    list.add(4);
    list.add(2);
    list.add(3);
    System.out.println("Original List: " + list);

    Collections.shuffle(list);

    System.out.println("Shuffled List: " + list);
    int number1 = list.remove(0);  // Remove the first value
    System.out.println("Number removed: " + number1);

    Collections.shuffle(list);

    System.out.println("Shuffled List: " + list);
    number1 = list.remove(0);
    System.out.println("Number removed: " + number1);

OUTPUT: -

Original List: [1, 4, 2, 3]
Shuffled List: [4, 3, 1, 2]
Number removed: 4
Shuffled List: [1, 3, 2]
Number removed: 1

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2nd Way: -

A better way would be to generate a random number from 0 to the size of the list, and get the value of that index and remove it.

int size = list.size();
Random random = new Random();

for (int i = 0; i < size; i++) {    
    int index = random.nextInt(list.size());
    int number1 = list.remove(index);
    System.out.println(number1);
}

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NOTE: - If you want to exclude a fixed set of numbers from being generated, then you can have those numbers in a list. And then remove all elements of that list from your list of numbers. And then use any of the approach above.