feat: add ruby codes - chapter tree (#1288)

codes/ruby/chapter_tree/binary_tree_dfs.rb

@@ -0,0 +1,62 @@
+=begin
+File: binary_tree_dfs.rb
+Created Time: 2024-04-18
+Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
+=end
+
+require_relative '../utils/tree_node'
+require_relative '../utils/print_util'
+
+### 前序遍历 ###
+def pre_oder(root)
+  return if root.nil?
+
+  # 访问优先级：根节点 -> 左子树 -> 右子树
+  $res << root.val
+  pre_oder(root.left)
+  pre_oder(root.right)
+end
+
+### 中序遍历 ###
+def in_order(root)
+  return if root.nil?
+
+  # 访问优先级：左子树 -> 根节点 -> 右子树
+  in_order(root.left)
+  $res << root.val
+  in_order(root.right)
+end
+
+### 后序遍历 ###
+def post_order(root)
+  return if root.nil?
+
+  # 访问优先级：左子树 -> 右子树 -> 根节点
+  post_order(root.left)
+  post_order(root.right)
+  $res << root.val
+end
+
+### Driver Code ###
+if __FILE__ == $0
+  # 初始化二叉树
+  # 这里借助了一个从数组直接生成二叉树的函数
+  root = arr_to_tree([1, 2, 3, 4, 5, 6, 7])
+  puts "\n初始化二叉树\n\n"
+  print_tree(root)
+
+  # 前序遍历
+  $res = []
+  pre_oder(root)
+  puts "\n前序遍历的节点打印序列 = #{$res}"
+
+  # 中序遍历
+  $res.clear
+  in_order(root)
+  puts "\nn中序遍历的节点打印序列 = #{$res}"
+
+  # 后序遍历
+  $res.clear
+  post_order(root)
+  puts "\nn后序遍历的节点打印序列 = #{$res}"
+end