Question about Random Number Generation...

[KiranKumar Gogineni]

Hi,
I need to generate 10 random numbers without repeating the same number again. This is what I need to achieve: I have a set of 100 questions and each time the test taker wants to take a test, the program should generate 10 questions from the available 100 question set. So, far i am able to generate random numbers without zero in the following way. But, how to avoid repeating the same number again? Any ideas or code will be appreciated.

import java.util.Random;

public class RandomTest
{
public static void main(String args[])
{
Random generator = new Random();
int rnumber = generator.nextInt( 100 )+1;
// what is the code to eliminate the repetition...?
System.out.println("Random Number: "+ rnumber);

}

}
[ May 23, 2006: Message edited by: KiranKumar Gogineni ]

[Keith Lynn]

What about using some kind of Collection? You can check to see if a Collection already contains an element.

[KiranKumar Gogineni]

I am a newbie to Collections. Could you please outline the psuedocode or approximate code so that I can explore the exact collection and try to implement?
Thanks for your idea.
Regards,
Kiran

[Michael Dunn]

> I have a set of 100 questions

use Collections.shuffle(..) to mix 'em up,
then take the first 10 from your set

[Garrett Rowe]

Alternatively, you can take advantage of the fact that collections that implement the Set interface don't allow duplicates:

instantiate a new Set
while (number of elements in the Set < 10)
   add a random question to the Set

[ May 23, 2006: Message edited by: Garrett Rowe ]

[Keith Lynn]

And if you use a TreeSet, they will be ordered.

[KiranKumar Gogineni]

Thanks a lot for your ideas. I will try to implement it. In the meanwhile, if anybody happened work on this kind of logic, please send me the code snippet that uses collections.
Regards,
Kiran

[Michael Dunn]

here's a simple shuffle

    
import java.util.*;
class Testing
{
  List list = new ArrayList();
  public Testing()
  {
    for(int x = 0; x < 100; x++) list.add(new Integer(x));
    Collections.shuffle(list);
    for(int x = 0, y = list.size(); x < y; x++) System.out.println(list.get(x));
  }
  public static void main(String[] args){new Testing();}
}

[Garrett Rowe]

And here's an example using a Set

public class UniqueElements
{
   private Set<Integer> theSet = new HashSet<Integer>();
   private Random generator = new Random();
 
   public UniqueElements(int desiredSize)
   {
      final int MAX = 100;
      while (theSet.size() < desiredSize)
      {
         theSet.add(generator.nextInt(MAX) + 1);
      }
      for (Integer e : theSet)
      {
         System.out.println(e);
      }
   }
 
   public static void main(String[] args)
   {
      new UniqueElements(10);
   }
}

[Mallesham Karnati]

Kiran,
Try this. It will serve your purpose.

import java.util.*;
class ShuffleTest
{

public static void main(String[] args)
{
ArrayList<Integer> list = new ArrayList<Integer>();

for(int x = 1; x < 101; x++)
{
list.add(Integer.valueOf(x)); //Adds 100 numbers to the list
}
Collections.shuffle(list); //This shuffles the list

for(int x = 0, y = 11; x < y; x++)
{
System.out.println(list.get(x)); //This gets the first 10 from the list
}
}


}

[KiranKumar Gogineni]

Thank you very much guys for your quick help.
Thanks a lot.
Kiran