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📜  C++ STL-Multiset

📅  最后修改于: 2020-10-19 01:13:36             🧑  作者: Mango

C++ STL Multiset

Multiset介绍

Multiset是C++ STL(标准模板库)的一部分。Multiset是类似于Set的关联容器，用于存储排序的值(该值本身是T类型的键)，但与Set仅存储唯一键的Set不同，multiset可以具有重复键。默认情况下，它使用<运算符比较键。

可以插入或删除多集中元素的值，但不能更改(元素始终为const)。

句法

template < class T,                             // multiset::key_type/value_type
           class Compare = less,        // multiset::key_compare/value_compare
           class Alloc = allocator         // multiset::allocator_type
           > class multiset;

参量

T：存储在容器多重集中的元素类型。

比较：比较类，它接受两个相同类型的布尔变量，并返回一个值。此参数是可选的，二进制谓词less是默认值。

Alloc：用于定义存储分配模型的分配器对象的类型。

例子1

让我们看一个示例来演示C++ Multiset：

#include 
#include 
#include 
#include 

using namespace std;

int main()
{
    multiset ms;
    multiset::iterator it, it1, msIt;
    int choice, item;   
    
    while (1)
    {
        cout<<"\n---------------------"<>choice;
        
        switch(choice)
        {
        case 1:
            cout<<"Enter value to be inserted: ";
            cin>>item;
            if (ms.empty())
                it1 = ms.insert(item);
            else
                it1 = ms.insert(it1, item);
            break;
        case 2:
            cout<<"Enter value to be deleted: ";
            cin>>item;
            ms.erase(item);
            break;
        case 3:
            cout<<"Enter element to find ";
            cin>>item;
            it = ms.find(item);
            if (it != ms.end())
                cout<<"Element found"<>item;
            cout<

输出：

---------------------
Multiset Example

---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 1
Enter value to be inserted: 100

---------------------
Multiset Example

---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 1
Enter value to be inserted: 200

---------------------
Multiset Example

---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 1
Enter value to be inserted: 300

---------------------
Multiset Example

---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 2
Enter value to be deleted: 200

---------------------
Multiset Example

---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 3
Enter element to find 100
Element found

---------------------
Multiset Example

---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 4
Enter element to be counted: 100
100 appears 1 times.

---------------------
Multiset Example

---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 5
Size of the Multiset: 2

---------------------
Multiset Example

---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 6
Elements of the Multiset:  100  300  

---------------------
Multiset Example

---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 7
The First Element of the Multiset is 100

---------------------
Multiset Example

---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 8

例子2

让我们看另一个示例来演示C++ Multiset：

#include 
#include 
#include 

using namespace std;

int main()
{
    // empty multiset container
    multiset  > ms1; 
    
    // insert elements in random order
    ms1.insert(400);
    ms1.insert(300);
    ms1.insert(600);
    ms1.insert(200);
    ms1.insert(500);
    ms1.insert(500); // 500 will be added again to the multiset unlike set
    ms1.insert(100);
    
    // printing multiset ms1
    multiset  :: iterator itr;
    
    cout << "\nMarks of ms1 class Room: "< ms2(ms1.begin(), ms1.end());
    
    // print all elements of the multiset ms2
    cout << "\nThe Number of students in class Room after assigning Class Room students: "<::iterator msIt1, msIt2;
    msIt1 =  ms1.begin();
    cout<< "\nHighest marks in ms1 Class Room: "<<*msIt1; 
    
    msIt2 =  ms2.begin();
    cout<< "\nHighest marks in ms2 Class Room: "<<*msIt2; 
        
    // remove all elements up to element with value 300 in ms2
    cout << "\n\nms2 Class Room after removal of Students less than 300 marks:\n ";
    ms2.erase(ms2.begin(), ms2.find(300));
    for (itr = ms2.begin(); itr != ms2.end(); ++itr)
    {
      cout << "  " << *itr;
    }
    
    // remove all elements with value 500 in ms2
    int num;
    num = ms2.erase(500);
    cout << "\n\nms2.erase(500) : ";
    cout << num << " removed \t" ;
    for (itr = ms2.begin(); itr != ms2.end(); ++itr)
    {
        cout << "  " << *itr;
    }
      
    cout << endl<

输出：

Marks of ms1 class Room: 
  600  500  500  400  300  200  100

The Number of students in class Room after assigning Class Room students: 
  100  200  300  400  500  500  600

Highest marks in ms1 Class Room: 600
Highest marks in ms2 Class Room: 100

ms2 Class Room after removal of Students less than 300 marks:
   300  400  500  500  600

ms2.erase(500) : 2 removed       300  400  600

ms1.lower_bound(400) : 400
ms1.upper_bound(400) : 300
ms2.lower_bound(400) : 400
ms2.upper_bound(400) : 600

会员职能

以下是多重集的所有成员函数的列表：

构造函数/析构函数

Functions Description
(constructor) Construct multiset
(destructor) Multiset destructor
operator= Copy elements of the multiset to another multiset.

迭代器

Functions Description
Begin Returns an iterator pointing to the first element in the multiset.
Cbegin Returns a const iterator pointing to the first element in the multiset.
End Returns an iterator pointing to the past-end.
cend Returns a constant iterator pointing to the past-end.
rbegin Returns a reverse iterator pointing to the end.
rend Returns a reverse iterator pointing to the beginning.
crbegin Returns a constant reverse iterator pointing to the end.
crend Returns a constant reverse iterator pointing to the beginning.

容量

Functions Description
empty Returns true if multiset is empty.
size Returns the number of elements in the multiset.
max_size Returns the maximum size of the multiset.

修饰符

Functions Description
insert Insert element in the multiset.
erase Erase elements from the multiset.
swap Exchange the content of the multiset.
clear Delete all the elements of the multiset.
emplace Construct and insert the new elements into the multiset.
emplace_hint Construct and insert new elements into the multiset by hint.

观察者

Functions Description
key_comp Return a copy of key comparison object.
value_comp Return a copy of value comparison object.

运作方式

Functions Description
find Search for an element with given key.
count Gets the number of elements matching with given key.
lower_bound Returns an iterator to lower bound.
upper_bound Returns an iterator to upper bound.
equal_range Returns the range of elements matches with given key.

分配者

Functions Description
get_allocator Returns an allocator object that is used to construct the multiset.

非成员重载函数

Functions Description
operator== Checks whether the two multisets are equal or not.
operator!= Checks whether the two multisets are equal or not.
operator< Checks whether the first multiset is less than other or not.
operator<= Checks whether the first multiset is less than or equal to other or not.
operator> Checks whether the first multiset is greater than other or not.
operator>= Checks whether the first multiset is greater than equal to other or not.
swap() Exchanges the element of two multisets.