Re: Math.random()

Lew <>
Mon, 25 Feb 2008 22:35:57 -0500
maya wrote:

oh brother... I think get gist of what you're saying.. will try
it....;) thank you very much.. (boolean array.... hmmm.. not sure if
I've ever even seen code for a boolean array...;)

  package testit;
  import java.util.Random;
  import java.util.Set;
  import java.util.HashSet;

  public class Scrambler
   private final Random rand = new Random();

   public Set <Integer> scrambleEggs( int upper, int count )
     Set <Integer> chosen = new HashSet <Integer> ( count * 4 / 3 + 1 );
     boolean [] selected = new boolean [ upper ];

     while ( count > 0 )
       int indx = rand.nextInt( upper );
       if ( ! selected [ indx ] )
         if ( chosen.add( indx ))
         selected [ indx ] = true;
     return chosen;

Untried, untested. (Pseudo-)Non-deterministic run time.

The bizarre reference to chosen.add()'s return value is a hint that one
doesn't really need the boolean array if one is using a Set, in that Set
guarantees uniqueness of its values with respect to equals(), and add() tells
you if the item was not already in the Set. This could really help if 'upper'
has a large value.

Things get trickier if you want multi-threaded use or a deterministic number
of times through the loop.


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