From: Bill Kelly <billk@...>
Date: 2008-08-18T09:18:10+09:00
Subject: Re: [QUIZ] Not So Random (#173)


Here's a "cheater" solution.  The sequences _are_ reproducible
via the #reset / #next API, for as long as a given instance of the 
Random object remains in existence.  However, independent instances
of the Random object, even if started with the same seed, won't
produce identical sequences.

Probably too stupid to post, but oh well..... :)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


class Random
  def initialize(ceiling=0, seed=nil)
    @ceiling = ceiling
    @seq = []
    @idx = 0
    srand(seed || (rand(0xFFFFFFFF) + 1))
  end

  def next
    unless @idx < @seq.length
      @seq.push( rand(@ceiling) )
      @idx = @seq.length - 1
    end
    
    n = @seq[@idx]
    @idx += 1
    n
  end
  
  def reset
    @idx = 0
  end
end


if $0 == __FILE__

require 'test/unit'

class RandomTest < Test::Unit::TestCase
  def test_001
    x = Random.new(100)
    y = Random.new(1000)

    xseq = Array.new(5) { x.next }
    yseq = Array.new(5) { y.next }

    xseq += Array.new(5) { x.next }
    yseq += Array.new(5) { y.next }

    x.reset
    assert_equal( xseq, Array.new(10) { x.next } )

    y.reset
    assert_equal( yseq, Array.new(10) { y.next } )
 
    xseq += Array.new(5) { x.next }
    yseq += Array.new(5) { y.next }

    x.reset
    assert_equal( xseq, Array.new(15) { x.next } )

    y.reset
    assert_equal( yseq, Array.new(15) { y.next } )
  end
end

end

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Regards,

Bill