feat: Add Ruby code - chapter "computational complexity" (#1212)

* feat: add ruby code - chapter computational complexity

* feat: add ruby code blocks

codes/ruby/utils/tree_node.rb

@@ -0,0 +1,18 @@
+=begin
+File: tree_node.rb
+Created Time: 2024-03-30
+Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
+=end
+
+### 二叉树节点类 ###
+class TreeNode
+  attr_accessor :val    # 节点值
+  attr_accessor :height # 节点高度
+  attr_accessor :left   # 左子节点引用
+  attr_accessor :right  # 右子节点引用
+
+  def initialize(val=0)
+    @val = val
+    @height = 0
+  end
+end