How can I generate a random number within a range but exclude some?

This is the most reliable way to do it.

Create an array with your range, remove all excluding elements

Choose a random index and return the value from that position.

public int getRandomNumber(int start, int end, List<Integer> excludingNumbers) {
 
    int[] range = IntStream.rangeClosed(start, end).toArray();
    List<Integer> rangeExcluding = Arrays.stream( range ).boxed().collect( Collectors.toList() );

    rangeExcluding.removeAll(list);
    int newRandomInt = new Random().nextInt(rangeExcluding.size())
 
    return rangeExcluding.get(newRandomInt);
}

Range includes start and end

example: val random = arrayOf((-5..-1).random(), (1..10).random()).random() In this example you exclude 0 in numbers between -5 and 10