tree_node.rb

class TreeNode
  attr_accessor :left, :right, :value

  def initialize(value)
    @value = value
  end

  # to be called on parent
  # for full tree
  def print
    flat = self.flatten

    Integer(Math.log2(flat.length + 1)).times do |i|
      row = flat.shift(2 ** i)
      puts row.to_s
    end
  end

  def flatten
    flat = [self]

    flat.each do |node|
      flat << node.left if node.left
      flat << node.right if node.right
    end
    flat
  end

  def to_s
    self.value
  end
end

a = TreeNode.new("a")
b = TreeNode.new("b")
c = TreeNode.new("c")
d = TreeNode.new("d")
e = TreeNode.new("e")
f = TreeNode.new("f")
g = TreeNode.new("g")

a.left, a.right = b, c
b.left, b.right = d, e
c.left, c.right = f, g
d.left, d.right = nil, nil
e.left, e.right = nil, nil
f.left, f.right = nil, nil
g.left, g.right = nil, nil

a.print