Generating random, unique values C#

Question

I\'ve searched for a while and been struggling to find this, I\'m trying to generate several random, unique numbers is C#. I\'m using System.Random, and I\'m us

Answer 1

I noted that the accepted answer keeps adding int to the list and keeps checking them with if (!randomList.Contains(MyNumber)) and I think this doesn't scale well, especially if you keep asking for new numbers.

I would do the opposite.

1. Generate the list at startup, linearly
2. Get a random index from the list
3. Remove the found int from the list

This would require a slightly bit more time at startup, but will scale much much better.

public class RandomIntGenerator
{
    public Random a = new Random();
    private List _validNumbers;

    private RandomIntGenerator(int desiredAmount, int start = 0)
    {
        _validNumbers = new List();
        for (int i = 0; i < desiredAmount; i++)
            _validNumbers.Add(i + start);
    }

    private int GetRandomInt()
    {
        if (_validNumbers.Count == 0)
        {
            //you could throw an exception here
            return -1;
        }
        else
        {
            var nextIndex = a.Next(0, _validNumbers.Count - 1);
            var number    = _validNumbers[nextIndex];
            _validNumbers.RemoveAt(nextIndex);
            return number;
        }
    }
}