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

codes/ruby/utils/tree_node.rb

@@ -16,3 +16,38 @@ class TreeNode
     @height = 0
   end
 end
+
+### 将列表反序列化为二叉数树：递归 ###
+def arr_to_tree_dfs(arr, i)
+  # 如果索引超出数组长度，或者对应的元素为 nil ，则返回 nil
+  return if i < 0 || i >= arr.length || arr[i].nil?
+  # 构建当前节点
+  root = TreeNode.new(arr[i])
+  # 递归构建左右子树
+  root.left = arr_to_tree_dfs(arr, 2 * i + 1)
+  root.right = arr_to_tree_dfs(arr, 2 * i + 2)
+  root
+end
+
+### 将列表反序列化为二叉树 ###
+def arr_to_tree(arr)
+  arr_to_tree_dfs(arr, 0)
+end
+
+### 将二叉树序列化为列表：递归 ###
+def tree_to_arr_dfs(root, i, res)
+  return if root.nil?
+
+  res += Array.new(i - res.length + 1) if i >= res.length
+  res[i] = root.val
+
+  tree_to_arr_dfs(root.left, 2 * i + 1, res)
+  tree_to_arr_dfs(root.right, 2 * i + 2, res)
+end
+
+### 将二叉树序列化为列表 ###
+def tree_to_arr(root)
+  res = []
+  tree_to_arr_dfs(root, 0, res)
+  res
+end