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

codes/ruby/chapter_tree/binary_tree_dfs.rb

@@ -8,13 +8,13 @@ require_relative '../utils/tree_node'
 require_relative '../utils/print_util'
 
 ### 前序遍历 ###
-def pre_oder(root)
+def pre_order(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)
+  pre_order(root.left)
+  pre_order(root.right)
 end
 
 ### 中序遍历 ###
@@ -47,7 +47,7 @@ if __FILE__ == $0
 
   # 前序遍历
   $res = []
-  pre_oder(root)
+  pre_order(root)
   puts "\n前序遍历的节点打印序列 = #{$res}"
 
   # 中序遍历