def von_neuman(seed=Time.now.nsec, sequence=[], vn_size=100)
  # generates a von_neuman pseudo-random sequence (array) using current date-time in nanoseconds as seed
  if sequence.size < vn_size
    y = (seed**2).digits
    z = y[y.size/2 - seed.digits.size/4, y.size/2 + seed.digits.size/4] 
    new_seed = z.join.to_i
    von_neuman(new_seed, sequence+z)
  else
    sequence
  end   
end

class Array
  def head
    self[0]
  end

  def tail
    self[1..-1]
  end

  def first_in_range(range)
    # returns a new array where the first element of this new array is included in 
    # such range e.g. [0,1,2,3,4,5].first_in_range(3..4) -> [3,4,5]
    range.include?(self.head) ? self : self.tail.first_in_range(range)
  end

end

def roll_dice(rs=[],rolls=1,sides=6,dice=[])
  rs = von_neuman if rs.size == 0 
  # Avoids the odd chance of not finding any 1..6 values in the random sequence by generating it again
  if rolls > 0
    x = rs.first_in_range(1..sides)
    roll_dice(x.tail,rolls-1,sides,dice.push(x.head))
  else
    dice
  end
end

def three_dice(rs=[])
  roll_dice(rs,3,6,[]).sum
end

# --- pseudo tests :) ------------

puts "Generating a Von Neuman pseudo-random series. First 24 elements"
puts von_neuman.inspect

puts "\n18 dice rolls \n#{roll_dice([],18,6,[])}\n"

puts "\n18 3d6\n"
18.times do
  |x|
  puts "#{x+1}.- #{three_dice}"
end