#! /usr/bin/env ruby

# Towers of Hanoi
# Copyright (C) 2000 by Michael Neumann (neumann@s-direktnet.de)
# This is public domain.
#

class Towers_of_Hanoi
  A = 0; B = 1; C = 2

  def initialize(n)
    # n = number of stack-elements of the tower
    @n = n
    @stack = []
    @stack[A] = (1..@n).to_a.reverse   # from
    @stack[B] = []                     # to
    @stack[C] = []                     # help
  end
 
  #
  # "from" and "to" are integers A,B or C.
  # n is the number of elements to put from stack "from" 
  # to stack "to" counted from the top of the stack
  #
  def move(from, to, n)
    if n == 1 then
      @stack[to].push(@stack[from].pop)
      output
    elsif n > 1 then
      help = ([A,B,C] - [from,to])[0]  # get help-stack
      move(from, help, n-1)
      move(from, to, 1)
      move(help, to, n-1)
    end
  end

  #
  # run the simulation
  #
  def run
    output
    move(A, B, @n)
  end

  #
  # override this method for user-defined output
  #
  def output
    p @stack
  end
  private :output

end

#
# test-program
#

if __FILE__ == $0
  print "Towers of Hanoi\n"
  print "---------------\n"
  print "Please input the height of the tower (e.g. 5): "
  n = readline.to_i

  toh = Towers_of_Hanoi.new(n)

  #
  # prints the three stacks out
  # and waits for keypress
  #
  def toh.output
    for i in 0..2 do
      print "abc"[i].chr, ": "
      p @stack[i]
    end
    readline
  end

  toh.run
end