How to Generate Non-Repeating Random Numbers in C#?

Generate unique random numbers in C#

In the development of applications that need to generate random unique numbers, developers often encounter problems with the System.Random class. Even if you use DateTime.Now.Ticks as a seed, there may still be duplicate numbers.

Solve duplicate value problem

System.Random.Next() itself does not guarantee the uniqueness of the generated numbers. When combined with a narrower range (e.g. 0 to 10), the probability of encountering duplicate values ​​is higher.

Alternative: List Maintenance

To overcome this limitation, a more robust approach is to maintain a list of generated numbers. Duplication can be avoided by checking whether the potential number already exists in the list.

The following is a modified implementation using this strategy:

<code class="language-csharp">public Random a = new Random();
public List<int> randomList = new List<int>();
int MyNumber = 0;

private void NewNumber()
{
    MyNumber = a.Next(0, 10);
    if (!randomList.Contains(MyNumber))
        randomList.Add(MyNumber);
}</code>

This approach ensures the creation of truly unique values ​​by maintaining a list of generated numbers and filtering out duplicates.

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