From: Wilson Bilkovich <wilsonb@...>
Date: 2006-03-17T06:20:34+09:00
Subject: Re: Card tricks with Ruby

On 3/16/06, grrr <grrr@toto.maatti> wrote:
> So suppose you have a deck of cards, that might have some number of cards.
>
> First the cards are shuffled, in effect placed in random order.
>
> Then the deck is split, ie. some number of cards are lifted from the top
> of the deck and placed under the remaining cards.
>
> How would one implement this? I was thinking of using an array, but how to
> shuffle the deck, and how to split the deck?
>

How about this as a starting point?

class Card
  attr_reader :card_id
  def initialize(card_id)
    @card_id = card_id
  end
end

class Deck
  attr_reader :cards
  def initialize(card_count = 52)
    @cards = []
    card_count.times {|i| @cards << Card.new(i)}
    shuffle
  end
  def shuffle
    @cards.sort! {rand}
  end
  def cut(offset = nil)
    top = @cards[0,(offset || @cards.length / 2)]
    @cards = (@cards - top) + top
  end
end

deck.cut defaults to cutting the deck in half.  deck.cut(5) takes the
top 5 cards and puts them on the bottom of the deck.
In real life, the attr_reader is bad form, because it exposes the
implementation of '@cards' to clients.  You don't really want people
shuffling the deck without calling Deck#shuffle.
To fix that, you could make custom accessors, like:
each_card, card_at(position), deal_card, etc.