[C++] STL container - multiset container (std::multiset container introduction | std::multiset container common operation api introduction)

1. mulset container

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1. Introduction to std::multiset container

In the Standard Template Library (STL, Standard Template Library) of the C++ language, the std::multiset container is provided.

• The key values ​​of elements in this container can be repeated;
• The elements in this container are ordered and sorted according to the specified rules;

When inserting an element into the std::multiset container , there is no need to verify whether the element already exists in the collection. It is directly inserted into the specified position according to the sorting rules;

The std::multiset container does not support inserting elements at the specified position;

The std::multiset container also does not support direct access to elements using subscript positions;

Before using the std::multiset container, you need to import the set header file;

#include "set"

Containers similar to set containers include multiset containers. The only difference is that elements in a set can only appear once, while elements in a multiset can appear multiple times;

The elements in the std::multiset container cannot be modified directly, the original elements can only be deleted first, and then new elements can be inserted;

2. Code example - multiset container

In the following code, a multiset container is created to store repeated elements;

multiset<int> myMultiSet = {
    
     1, 2, 3, 4, 5, 4, 3, 2, 1 };

When the above container is initialized, the elements in the container will be automatically sorted. The sorted order is as follows:

1 1 2 2 3 3 4 4 5

Code example:

#include "iostream"
using namespace std;
#include "set"

int main() {
    
    

    // 初始化 multiset 容器
    multiset<int> myMultiSet = {
    
     1, 2, 3, 4, 5, 4, 3, 2, 1 };

    // 遍历打印 multiset 中的所有元素  
    for (auto& elem : myMultiSet) {
    
    
        cout << elem << " ";
    }
    cout << endl;


	// 控制台暂停 , 按任意键继续向后执行
	system("pause");

	return 0;
};

Results of the :

1 1 2 2 3 3 4 4 5
请按任意键继续. . .

2. Introduction to the common operation API of std::multiset container

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1. Introduction to commonly used APIs

Common operations of std::multiset containers: The interfaces of std::multiset containers and std::set containers are basically the same;

• insert(): Insert one or more elements into the multiset container;
• erase(): delete one or more elements in the multiset container;
• clear(): Clear all elements in the multiset container;
• find(): Find a specific element in the multiset container;
• count(): Returns the number of specific elements in the multiset container . This function can only return 0 or 1 in the set container, which is meaningful in the multiset container;
• lower_bound(): Returns the range of elements in the multiset container that are greater than or equal to the given key value;
• upper_bound(): Returns the range of elements in the multiset container that are greater than the given key value;
• equal_range(): Returns the range of elements in the multiset container that are equal to the given key value;

2. Code examples - common operations of multiset containers

Code example:

#include "iostream"
using namespace std;
#include "set"

void printMS(multiset<int>& ms) {
    
    
    // 遍历打印 multiset 中的所有元素  
    for (auto& elem : ms) {
    
    
        cout << elem << " ";
    }
    cout << endl;
}


int main() {
    
    

    // 初始化 multiset 容器
    multiset<int> myMultiSet = {
    
     1, 2, 3, 4, 5, 4, 3, 2, 1 };
    // 遍历打印容器
    printMS(myMultiSet);

    // 插入元素
    myMultiSet.insert(9);
    // 遍历打印容器
    cout << "插入元素 9 : ";
    printMS(myMultiSet);

    // 删除元素
    myMultiSet.erase(3);
    // 遍历打印容器
    cout << "删除元素 3 : ";
    printMS(myMultiSet);

    // 获取元素数量
    int count = myMultiSet.count(2);
    // 遍历打印容器
    cout << "元素 2 个数 : " << count << endl;
    printMS(myMultiSet);

    // 清空元素
    myMultiSet.clear();
    // 遍历打印容器
    cout << "清空元素 : ";
    printMS(myMultiSet);

	// 控制台暂停 , 按任意键继续向后执行
	system("pause");

	return 0;
};

Results of the :

1 1 2 2 3 3 4 4 5
Insert element 9: 1 1 2 2 3 3 4 4 5 9 Delete
element 3: 1 1 2 2 4 4 5 9
Number of elements 2: 2
1 1 2 2 4 4 5 9
Clear Element:
Please press any key to continue. . . .