Bug fixes and improvements (#1298)

* Fix is_empty() implementation in the stack and queue chapter

* Update en/CONTRIBUTING.md

* Remove "剩余" from the state definition of knapsack problem

* Sync zh and zh-hant versions

* Update the stylesheets of code tabs

* Fix quick_sort.rb

* Fix TS code

* Update chapter_paperbook

* Upload the manuscript of 0.1 section

* Fix binary_tree_dfs.rb

* Bug fixes

* Update README

* Update README

* Update README

* Update README.md

* Update README

* Sync zh and zh-hant versions

* Bug fixes

zh-hant/codes/ruby/utils/tree_node.rb

@@ -16,3 +16,38 @@ class TreeNode
     @height = 0
   end
 end
+
+### 將串列反序列化為二元數樹：遞迴 ###
+def arr_to_tree_dfs(arr, i)
+  # 如果索引超出陣列長度，或者對應的元素為 nil ，則返回 nil
+  return if i < 0 || i >= arr.length || arr[i].nil?
+  # 構建當前節點
+  root = TreeNode.new(arr[i])
+  # 遞迴構建左右子樹
+  root.left = arr_to_tree_dfs(arr, 2 * i + 1)
+  root.right = arr_to_tree_dfs(arr, 2 * i + 2)
+  root
+end
+
+### 將串列反序列化為二元樹 ###
+def arr_to_tree(arr)
+  arr_to_tree_dfs(arr, 0)
+end
+
+### 將二元樹序列化為串列：遞迴 ###
+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
+
+### 將二元樹序列化為串列 ###
+def tree_to_arr(root)
+  res = []
+  tree_to_arr_dfs(root, 0, res)
+  res
+end