Tag-hash table

1. Knowledge points

Basic knowledge of hash table:
https://blog.csdn.net/u011109881/article/details/80379505

Use of unordered_set of C++ STL (including unordersd_map):
https://blog.csdn.net/qq_32172673/article/details/85160180

Two, programming questions

2.1 The first round (easy)

#771 Gems and stones

#1748 Sum of unique elements

#1002Find common characters

#1207 Unique number of appearances