#! /usr/local/bin/ruby

def time
  start = Time.now
  result = yield
  diff = Time.now - start
  puts "Elapsed time: #{diff} secs"
  p result
end

def make_cache(arity)
  seed = "{}"
  (arity - 1).times do
    seed = "Hash.new { |hash, key| hash[key] = #{seed} }"
  end
  eval(seed)
end

class Tarai
  def initialize
    @cache = make_cache(3)
  end

  def call(x, y, z)
    return y if x <= y
    @cache[x][y][z] ||= call(
      call(x - 1, y, z),
      call(y - 1, z, x),
      call(z - 1, x, y)
    )
  end
end

tarai = Tarai.new

time { tarai.call(100, 50, 0) }