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/docs/chapter_tree/array_representation_of_tree.md

@@ -123,7 +123,9 @@
 === "Ruby"
 
     ```ruby title=""
-
+    ### 二元樹的陣列表示 ###
+    # 使用 nil 來表示空位
+    tree = [1, 2, 3, 4, nil, 6, 7, 8, 9, nil, nil, 12, nil, nil, 15]
     ```
 
 === "Zig"