Non repeating random numbers

Question

As a part of my project I need to create non repeating 2 or 3 digit random numbers by giving a set of numbers. I don't want to implement a list or array for that, since I should get 1 random number for each function call.

I tried to do that using SecureRandom class of Java. I got help from some of the sites as well, but I am stuck in between, can we shuffle the VALUES and get it done? But I don't know how that could be done. Can anyone help me?

import java.security.SecureRandom;
public class RandomNumber {
private static final RandomNumber rnd= new RandomNumber();

    private static final char[] VALUES = new char[] {
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};  
     private static final SecureRandom srn= new SecureRandom();
     public String createID()
     { 
       byte[] bytes = new byte[3]; 
       srn.nextBytes(bytes);

     }

Answer 1

Fisher-yates shuffle algorithm is the way to go. Its efficient for shuffling. and it works in linear time.

here is algo

To shuffle an array a of n elements:
  for i from n − 1 downto 1 do
       j ← random integer with 0 ≤ j ≤ i
       exchange a[j] and a[i]

and the code

for(int i=VALUES.length-1; i>0; i--){
            int rand = (int) (Math.random()*i);
            char temp = VALUES[i];
            VALUES[i] = VALUES[rand];
            VALUES[rand] = temp;
    }