print-edge.rb

#!/usr/bin/env ruby

class Node
  attr_accessor :data, :left, :right

  def initialize(data, left = nil, right = nil)
    @data = data
    @left = left
    @right = right
  end

  def self.from_array(array)
    array ? self.new(array.shift, from_array(array.shift), from_array(array.shift)) : nil
  end

  def inspect
    "[#{data}, #{left.inspect}, #{right.inspect}]"
  end
end

data = [30,
        [20,
          [10, [5], [15]],
          [25, nil, [28]]],
        [40,
          [35],
          [50, [41]]]]

tree = Node.from_array(data)

def print_edge(tree)
  puts(tree.data)
  print_left_edge(tree.left)
  print_right_edge(tree.right)
end

def print_left_edge(tree)
  return unless tree
  puts(tree.data)
  print_left_edge(tree.left)
  print_end(tree.right)
end

def print_right_edge(tree)
  return unless tree
  print_end(tree.left)
  print_right_edge(tree.right)
  puts(tree.data)
end

def print_end(tree)
  return unless tree
  if !tree.left && !tree.right
    puts tree.data
  end
  print_end(tree.left)
  print_end(tree.right)
end

print_edge(tree)