Generate random numbers in loop without repeating.

See my tip: "Random extraction of 5 cards from a deck"[^], it is C++ but you should get the idea.

The first solution may work, but it will start to become slower the more numbers were already chosen. (after all, after having 4999 numbers selected there is only one possibility, but it may be generating any value, needing to try again, and again, and again).

One thing that may make it faster is using a HashSet instead a list, as searching in a HashSet is faster. But my real solution is different.

First we create a list which all possible values.

List<int> available = new List<int>(5000);
for(int i=1; i<=5000; i++)
  available.Add(i);

Then, we will keep generating random indexes (instead of random values). Such indexes will be used to get the value from the available list, put it in the result and then remove it from the available list.

List<int> result = new List<int>(5000);
while(available.Count > 0)
{
  int index = random.Next(availableCount);
  result.Add(available[index]);
  available.RemoveAt(index);
}

return result;

This way, if you create a list with 1 million values, you will have only 1 million calls to random.Next();
Surely the list itself has its own problems, but it is better than keep waiting until the last available number is guess.

Try this snippet

private static List<int> Randomize(int count, int min, int max)
        {
            Random r = new Random();
            List<int> result = new List<int>();
            if (count < max - min)
            {
                while (result.Count <= count)
                {
                    int number = r.Next(min, max);
                    if (!result.Contains(number))
                    {
                        result.Add(number);
                    }
                }
            }
            else
            {
                Console.WriteLine("Select another boundaries or number count");
            }
            return result;
        }

I realise that this is an old question and I would not normally respond but I feel that the best solution has not been explored. It seems to me that the question is asking for a method that shuffles a data set. There is a well established algorithm that does this called the Fisher-Yates Shuffle. Here is an implementation in C#.

private static void FisherYatesShuffle<T>(IList<T> list)
       {
           int count = list.Count;
           var random = new Random();

           for (int i = 0; i < count; i++)
           {
                //Randomly set n to a value >=i but<count
               int n = random.Next(i, count);
               //swap the contents of list[n] with those of list[i]
               T temp = list[n];
               list[n] = list[i];
               list[i] = temp;
           }
       }

       private static void Main()
       {
           int[] list = Enumerable.Range(1, 50).ToArray();
           FisherYatesShuffle(list);
           foreach (int value in list)
           {
               Console.WriteLine(value);
           }
           Console.ReadLine();
       }

Link[^]

i'm colecting all solution and this is the result:

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Collections.Generic;

namespace WebApplication1
{
    public partial class _Default : System.Web.UI.Page
    {
        public static Random r=new Random();
        public static int number;
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void ASPxButton1_Click(object sender, EventArgs e)
        {
           //creat a text box in desing mode and call it ASPxTextBox1
            if (ASPxTextBox1.Text == "")
            {
                Response.Write("first enter you count number");
            }
            else
            {
                number = Convert.ToInt32(ASPxTextBox1.Text);
                List<int> available = new List<int>(number);
                for (int i = 1; i <= number; i++)
                    available.Add(i);
                List<int> result = new List<int>(number);
                while (available.Count > 0)
                {
                    int index = r.Next(available.Count);
                    result.Add(available[index]);
                    available.RemoveAt(index);
                }
                for (int i = 0; i < result.Count; i++)
                {
                    Response.Write(result[i] + "-");
                }
            }
        }

        protected int Pro_R(int min, int max)
        {
            return (r.Next(min, max));
        }
    }
}

I usaly use a globalized random number generator so my application dosen't load the same number combos repeatedly.
(place this in a global area)

static System.Random random = new Random();

Then you can make a list of ALL numbers in your target range and delete em as you muddle

public void d()
{
int TargetRange = 5000;
List<int> NumberPool = new List<int>();
for (int i = 0; i < TargetRange ; i++)
{
NumberPool.Add(i);
}

List<int> Muddle = new List<int>();
for (int i = 0; i < TargetRange ; i++)
{
int r = random.Next(0, NumberPool.Count);
Muddle.Add(r);
NumberPool.Remove(r); 
}
}

public string generatrnumber()
{

Random rnd = new Random();
int val;

string outstr = "";

for (int i = 0; i < 7; ++i)
{

val = rnd.Next(0, 62);

if (val < 26)

outstr += (char)(val + 'a');

else if (val < 52)

outstr += (char)('A' + (val - 26));

else
{

outstr += (char)('0' + (val - 52));

}

}
return outstr;
}

Try this it may improve speed of execution

Random random = new Random();
Hashtable ht = new Hashtable();
int totalItems = 5000;
int maxValue = totalItems + 1;

List<int> result = new List<int>(totalItems);
for (int x = 0; x < totalItems; x++)
{
    int index = random.Next(0, maxValue);
    while (ht[index] != null) index = random.Next(0, maxValue);
    result.Add(index);
    ht[index] = "1";
}
ht.Clear();

I thought I would add a one liner just for completeness.

var randomList = Enumerable.Range(1, 10).OrderBy(x => Guid.NewGuid());

This will result in a list of 10 randomized numbers ranging from 1 to 10
The OrderBy extension with Guid.NewGuid ensures that the list is always random regardless of how many times it count. (Taking in account of course the randomnize of a the NewGuid Method. see [^]