拼写修复；增加提问

Author: PegasusWang

docs/07_哈希表/hashtable.md

@@ -171,6 +171,7 @@ class HashTable(object):
 具体的实现和代码编写在视频里讲解。这个代码可不太好实现，稍不留神就会有错，我们还是通过编写单元测试验证代码的正确性。
 
 # 思考题
+- 请你分析下哈希表插入和删除元素的平均时间复杂度是多少？我们都实现代码了，相信这个问题你可以回答上来
 - Slot 在二次探查法里为什么不能直接删除？为什么我们要给它定义几个状态？
 
 # 延伸阅读

docs/08_字典/dict.md

@@ -23,7 +23,7 @@ class DictADT(HashTable):
     pass
 ```
 
-视频里我们将演示如何实现这些方法，并且写单侧验证正确性。
+视频里我们将演示如何实现这些方法，并且写单测验证正确性。
 
 # Hashable
 作为 dict 的 key 必须是可哈希的，也就是说不能是 list 等可变对象。不信你在 ipython 里运行如下代码：
@@ -36,11 +36,13 @@ d[[1]] = 1
 
 我引用 python 文档里的说法，大家可以自己理解下：
 
-> An object is hashable if it has a hash value which never changes during its lifetime (it needs a __hash__() method), and can be compared to other objects (it needs an __eq__() or __cmp__() method). Hashable objects which compare equal must have the same hash value.
+```
+An object is hashable if it has a hash value which never changes during its lifetime (it needs a __hash__() method), and can be compared to other objects (it needs an __eq__() or __cmp__() method). Hashable objects which compare equal must have the same hash value.
 
-> Hashability makes an object usable as a dictionary key and a set member, because these data structures use the hash value internally.
+Hashability makes an object usable as a dictionary key and a set member, because these data structures use the hash value internally.
 
-> All of Python’s immutable built-in objects are hashable, while no mutable containers (such as lists or dictionaries) are. Objects which are instances of user-defined classes are hashable by default; they all compare unequal (except with themselves), and their hash value is derived from their id().
+All of Python’s immutable built-in objects are hashable, while no mutable containers (such as lists or dictionaries) are. Objects which are instances of user-defined classes are hashable by default; they all compare unequal (except with themselves), and their hash value is derived from their id().
+```
 
 
 # 思考题：

docs/09_集合/set.md

@@ -1,5 +1,6 @@
 # 集合 set
 
+集合是一种不包含重复元素的数据结构，经常用来判断是否重复这种操作，或者集合中是否存在一个元素。
 这一章讲集合，实际上它的底层也是哈希表实现的，所以像实现 DictADT 一样，借助 HashTable 实现它也比较简单。
 
 
@@ -39,6 +40,9 @@ class SetADT(HashTable):
 
 
 # 思考题
+- 集合判断一个元素是否存在的时间复杂度是多少？
+- 集合的元素 key 需要满足什么概念？可变对象可以吗？
+- 请你在 SetADT 基础上实现集合的 remove 操作和 pop 操作
 - 你能尝试实现对称差操作吗？这里我没有实现，留给你作为练习
 - 你知道如何重载 python 的内置运算符吗？这里我们实现 set 的集合操作就是用到了重载，请阅读相关 python 文档。