Problem with randomize numbers

Question

3.67/5 (3 votes)

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Hello
I have a problem with random array. I need to have many randomize numbers but they have to be all dissimilar. If program generates 12, it must generate another number next time (not 12)!!!

I wrote this code:

C#

List<int> rn = new List<int>();
Random r = new Random();
bool br = true;

for (int p = 0; p < 10; p++)
{
    int i=0;
    while (true)
    {
        i = r.Next(1, 11);
        foreach (int a in rn)
        {
            if (a == i)
                br = false;
        }
        if (br == true)
            break;
    }
    rn.Add(i);
}

but after 4 or 5 numbers it is prolonging very bad.
help me please.:confused:

Posted 12-Feb-11 22:37pm

JosephineBarry

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Estys · Accepted Answer · 2011-02-12T22:47:00

Solution 2

You should set

br=true;

before the

foreach (int a in rn)

loop

addendum
Try this :

for (int p = 0; p < 10; p++)
{
    int i=0;
    while (true)
    {
        i = r.Next(1, 11);
        if (!rn.Contains(i))
        {
            rn.Add(i);
            break;
        }
    }
}

Cheers

Posted 12-Feb-11 22:47pm

Estys

Updated 12-Feb-11 23:06pm

v2

Comments

JosephineBarry 13-Feb-11 5:02am

Yes. I did it and it became much better thank you. but it is still prolonging with big numbers. example 10000

List<int> rn = new List<int>();Random r = new Random();bool br = true;

for (int p = 0; p < 10000; p++){ int i=0; while (true) {

i = r.Next(1, 10001); br = true;foreach (int a in rn)

{ if (a == i) br = false; }

if (br == true) break; } rn.Add(i);}but thank you.

Estys 13-Feb-11 5:07am

If you mean by "prolongs" "it takes a long time", see my updated answer.

JosephineBarry 13-Feb-11 5:16am

thanks
but it still takes a long time with big numbers.
sorry. :rose:

Shahin Khorshidnia 13-Feb-11 8:19am

Vote 5
(perspicacity)

Shahin Khorshidnia · Accepted Answer · 2011-02-12T22:46:00

Hi,
I've written a tip and I think it can help.

How to generate many random various numbers?[^]

briefly:

C#

//C#
public static int RandomNumber(ref List<int> numbers, Random random)
{
    int count = numbers.Count;
    int randomIndex = random.Next(0, count);
    int returnedNumber = numbers[randomIndex];
    numbers.RemoveAt(randomIndex);
    return returnedNumber;
}

It's requisite for using the method, to have a random variable and a list of numbers, for example:

//C#
Random random = new Random();
List<int> numbers = new List<int>();
for (int i = 0; i <= 1000; i++)
{
    numbers.Add(i);
}
//Ok, For each using the method, there is a new and defferent random number:
Console.WriteLine(RandomNumber(ref numbers, random));
Console.WriteLine(RandomNumber(ref numbers, random));
Console.WriteLine(RandomNumber(ref numbers, random));
Console.WriteLine(RandomNumber(ref numbers, random));
Console.WriteLine(RandomNumber(ref numbers, random));
Console.ReadKey();

And I think you'll see a good performance.