constrained_towers.rb

class ConstrainedTowers < Towers
  def initialize discs
    super
    @ternary = ConstrainedTowers.ternarise @count, @discs
    @directions = {}
    @stacks[0].each do |disc|
      @directions[disc] = :right
    end
  end

  def move
    @flip = Towers.diff ConstrainedTowers.ternarise(@count, @discs),
                       ConstrainedTowers.ternarise(@count += 1, @discs)
    @source = find_disc

    @stacks[find_stack].push @stacks[@source].pop
  end

  def find_disc
    @stacks.each_with_index do |stack, index|
      return index if stack.index @flip
    end
  end

  def find_stack
    case @source
    when 0
      @directions[@flip] = :right
      return 1
    when 2
      @directions[@flip] = :left
      return 1
    when 1
      if @directions[@flip] == :right
        return 2
      else
        return 0
      end
    end
  end

  def binary
    ternary
  end

  def ternary
    ConstrainedTowers.ternarise @count, @discs
  end

  def solved
    ternary.chars.all? { |trit| trit.to_i == 2 }
  end

  def inspect
    {
      stacks: @stacks,
      count: ternary
    }
  end

  def ConstrainedTowers.ternarise value, width
    '%0*d' % [width, value.to_s(3)]
  end
end