From: Eric Hodel <drbrain@...7.net>
Date: 2011-07-22T08:37:24+09:00
Subject: Re: Building a tree from the leaves down

On Jul 21, 2011, at 8:21 AM, Intransition wrote:
> Basic example, let's use this class:
> 
>  class CaseObject
>    attr :case
>    def initialize(parent_case)
>      @case = parent_case
>    end
>  end
> 
> And this has been defined:
> 
>  c1 = CaseObject.new(nil)
>  c11 = CaseObject.new(c1)
>  c12 = CaseObject.new(c1)
>  c121 = CaseObject.new(c12)
>  c122 = CaseObject.new(c12)
>  d1 = CaseObject.new(nil)
>  d11 = CaseObject.new(d1)
>  d12 = CaseObject.new(d1)

This is already a tree.

> Then I am given all the _leaf_ nodes in a list:
> 
>  [c11, c121, c122, d11, d12]

You won't need to rebuild the original tree if you have bidirectional links.

class CaseObject
  def initialize parent
    @case = parent
    @children = []
    parent.add self if parent
  end

  def add child
    @children << child
  end
end

Walking the tree up or down is simple when you can walk both up and down so the exercise is left to the reader.

Also, there's no relationship between the d nodes and the c nodes.