Non-repetitive random number

Question

To generate Random numbers from 1- 20 I need to pick selective and it should not be repetitive.

How to do this in C#

Note I need to loop through as like this

Answer 1

Just like i did:

    list.Clear();
    int count = 0;
    
    while (count < 20)
    {            
        int x = Random.Range(1, 21);
        if (!list.Contains(x))
        {
            list.Add(x);
            count++;
        }
    }

Answer 2

class Program
{
    static void Main(string[] args)
    {        
        List<int> list = new List<int>();
        int val;
        Random r;
        int IntialCount = 1;
        int count = 7 ;
        int maxRandomValue = 8;

        while (IntialCount <= count)
        {
            r = new Random();
            val = r.Next(maxRandomValue);
            if (!list.Contains(val))
            {
                list.Add(val);
                IntialCount++;
            }

        } 
    }
}

Answer 3

static void Main(string[] args)
{
    //Randomize 15 numbers out of 25 - from 1 to 25 - in ascending order
    var randomNumbers = new List<int>();
    var randomGenerator = new Random();
    int initialCount = 1;

    for (int i = 1; i <= 15; i++)
    {
        while (initialCount <= 15)
        {
            int num = randomGenerator.Next(1, 26);
            if (!randomNumbers.Contains(num))
            {
                randomNumbers.Add(num);
                initialCount++;
            }
        }
    }
    randomNumbers.Sort();
    randomNumbers.ForEach(x => Console.WriteLine(x));
}

Answer 4

This method will generate all the numbers, and no numbers will be repeated:

/// <summary>
/// Returns all numbers, between min and max inclusive, once in a random sequence.
/// </summary>
IEnumerable<int> UniqueRandom(int minInclusive, int maxInclusive)
{
    List<int> candidates = new List<int>();
    for (int i = minInclusive; i <= maxInclusive; i++)
    {
        candidates.Add(i);
    }
    Random rnd = new Random();
    while (candidates.Count > 0)
    {
        int index = rnd.Next(candidates.Count);
        yield return candidates[index];
        candidates.RemoveAt(index);
    }
}

You can use it like this:

Console.WriteLine("All numbers between 0 and 20 in random order:");
foreach (int i in UniqueRandom(0, 20)) {
    Console.WriteLine(i);
}