How to Serialize/Deserialize a binary tree

serialize-tree.rb

# Binary tree
# 1. value (int)
# 2. left node (Tree or nil)
# 3. right node (Tree or nil)

class Tree
  attr_accessor :value
  attr_accessor :left_node
  attr_accessor :right_node
  
  def initialize(value, left_node, right_node)
    self.value = value
    self.left_node = left_node
    self.right_node = right_node
  end
end

def serialize(tree)
  return 'null' if tree.nil?

  [
    "#{tree.value}",
    serialize(tree.left_node),
    serialize(tree.right_node)
  ].join(',')
end

def deserialize(s)
  pieces = s.split(',')
  deserialize_internal(pieces)
end

def deserialize_internal(pieces)
  return nil if pieces.empty?
  if pieces[0] == 'null'
    pieces.delete_at(0)
    return nil
  end

  n = Tree.new(pieces[0].to_i, nil, nil)
  pieces.delete_at(0)

  n.left_node = deserialize_internal(pieces)
  n.right_node = deserialize_internal(pieces)

  n
end

# Example 1:
#
#           11
#      2            3
# null   4    null    null
#
# Preorder
# 11,2,null,4,null,null,3,null,null

# Example 2:
#
#           11
#      2            3
# null   4    null    null
#      5  null
#  null null
#
# Preorder
# 11,2,null,4,5,null,null,null,3,null,null

n4 = Tree.new(4, nil, nil)
n2 = Tree.new(2, nil, n4)
n3 = Tree.new(3, nil, nil)
t = Tree.new(11, n2, n3)

s = serialize(t)
puts s

dt = deserialize(s)
s2 = serialize(dt)
puts s2