LeetCode Series articles

One 、 Title Description

   Give you a string $jewels$ Represents the type of gem in stone , Another string $stones$ Represents the stone you have .$stones$ Each character in represents a type of stone you have , You want to know how many stones you have are gems .

Be careful ：

• $jewels$ and $stones$ It consists of only English letters .
• $jewels$ All characters in are unique .
• Letters are case sensitive , therefore $a$ and $A$ It's different types of stones .

Two 、 Example

   Input ： jewels = “aA”, stones = “aAAbbbb”
   Output ： 3

3、 ... and 、 Main idea

   The meaning of the question is very clear , Is to count the number of gemstones in the stone . We can choose to traverse the string directly $stones$, Judge whether each stone is a gem in turn , If so, include it in the count , Finally, you can get the number of gemstones . We can also traverse the string first $stones$, Count the number of occurrences of each stone , And then traverse the string $jewels$, Judge whether each gem has appeared in the stone in turn , If so, add the number of occurrences of the stone to the count , Finally, you can get the number of gemstones .

Four 、 Code implementation

1、 utilize unordered_set Containers

   If we are directly traversing the string $stones$ Judge whether each stone is a gem , Finally get the number of gemstones , Then we can store the type of gem in unordered_set The container , When judging whether a stone is a gem, you can unordered_set Look in the container , If found, it means that the stone is a gem .
 
The code is as follows ：

2、 utilize unordered_map Containers

   If we traverse first $stones$ character string , Count the number of occurrences of each stone , At this point, we can store the stone and its occurrence times in unordered_map The container , And then traverse the string $jewels$, If $jewels$ A character in a string is in $stones$ There has been , The character is placed in $stones$ The number of occurrences in adds up to $count$ among , Finally, you can get the number of gemstones .
 
The code is as follows ：