KornyHanoi.rb

class KornyHanoi
  def initialize(options={:discs => 8})
    @discs = options[:discs]
    @all_pegs = [:from, :pivot, :to]
    @pegs = {:from => [], :to => [], :pivot => []}
    @discs.downto(1) do |num|
      @pegs[:from] << num
    end
  end

  def solve
    print_state
    one_peg = :from
    clockwise = {:from => :pivot, :pivot => :to, :to => :from}
    anticlockwise = {:from => :to, :pivot => :from, :to => :pivot}
    one_move = @discs % 2 == 0 ? clockwise : anticlockwise

    while !complete?
      # move the 'one' disc
      next_one_peg = one_move[one_peg]
      shift(:from => one_peg, :to => next_one_peg)
      one_peg = next_one_peg
      print_state
      break if complete?

      # and make the only legal move - assume an order of the remaining pegs:
      from_peg, to_peg = @all_pegs - [one_peg]
      # is this order ok?
      if @pegs[from_peg].last == nil || ( @pegs[to_peg].last != nil && @pegs[from_peg].last > @pegs[to_peg].last )
        # if not, swap order
        from_peg, to_peg = to_peg, from_peg
      end
      shift(:from => from_peg, :to => to_peg)
      print_state
    end
  end

  def complete?
    @pegs[:to].length == @discs
  end

  def shift(params)
    from = params[:from]
    to = params[:to]
    raise "from peg (#{from}) is empty!" if @pegs[from].empty?
    @pegs[to].push @pegs[from].pop
  end

  def print_state
    puts @pegs.inspect
  end

end

KornyHanoi.new(:discs => 9).solve