谁给解释一下，后两个正则表达式是什么意思

race — Sat, 10 Mar 2012 01:10:18 +0800

'12345678'.slice(/.*(?=567)/)
# => "1234" 
'12345678'.slice(/(?<=123).*/)
# => "45678" 
'12345678'.slice(/(?!123).*/)
# => "2345678" 
'12345678'.slice(/.*(?<!567)/)
# => "12345678" 
'12345678'.slice(/.*(?<!5678$)/)
# => "1234567"

[Ruby Quiz] 针对代码片段，提点改进意见吧

race — Sun, 04 Mar 2012 04:15:26 +0800

最近面试，要求解决如下小问题模拟超市收银台的工作流程，商品价格可以单价和 package 价格例如：

Product Code | Price

A | $2.00 each or 4 for $7.00 B | $12.00 C | $1.25 or $6 for a six pack D | $0.15 实现工作流如下： terminal.setPricing(...) terminal.scan("A") terminal.scan("C") ... etc. result = terminal.total 显示结果： Scan these items in this order: ABCDABAA; Verify the total price is $32.40. Scan these items in this order: CCCCCCC; Verify the total price is $7.25. Scan these items in this order: ABCD; Verify the total price is $15.40. 我的代码如下：

class Terminal
  attr_accessor :item_types, :item_sequence

  def initialize
    self.item_types = []
    self.item_sequence = []
  end

  #input product name and price.
  #can be only unit price or both unit price and volume price
  #
  #@terminal.set_price 'A', 3.00
  #@terminal.set_price 'A', 3.00, 5, 13.00
  def set_price p_code, *price
    p_class = item_exists?(p_code) ? eval("#{p_code}") : create_item(p_code) 
    p_class.send :unit_price=, price[0]
    p_class.send :volume_price=, {amount: price[1], v_price: price[2]} unless price[1].nil? || price[2].nil? 
  end

  def scan p_code
    eval "#{p_code}.new"
    self.item_sequence << p_code
  end

  def total_cost
    self.item_types.inject(0.0){|sum,item| sum += Item.cost(item)}
  end

  private
  def create_item p_code
    Object.const_set p_code, Class.new( Item )
    p_class = eval "#{p_code}"
    p_class.amount = 0
    p_class.scaned_items = []
    self.item_types << p_class
    p_class
  end
  def item_exists? p_name
    eval "defined?(#{p_name}) && #{p_name}.is_a?(Class)"
  end
end

class Item
  class << self; attr_accessor :unit_price, :volume_price, :amount, :scaned_items; end
  attr_accessor :item_name

  def initialize
    self.class.amount += 1
    self.class.scaned_items << self
    self.item_name = "#{self.class}_#{self.class.amount}" 
  end

  protected
  def self.cost item
    return 0 if item.amount == 0
    if item.volume_price.nil?
      item.amount * item.unit_price
    else
      item.unit_price * (item.amount % item.volume_price[:amount]) + 
      item.volume_price[:v_price] * (item.amount / item.volume_price[:amount]).to_i
    end
  end
end

race (Race)

谁给解释一下，后两个正则表达式是什么意思

[Ruby Quiz] 针对代码片段，提点改进意见吧

Product Code | Price