stl set是无序的

In this tutorial you will learn about stl unordered set container in c++ and various functions applicable on it.

在本教程中，您将学习c ++中的stl无序集合容器以及适用于它的各种功能。

Unordered Set comes under unordered containers. As we discussed in , unordered containers internally implemented with hash tables. Each item calculated by hash function, to map to . The main advantage is if we have effective hash function we can find elements in O (1) time. On average it can go to linear time. Simply we can say it’s based on type of hash function used.

无序集位于无序容器下。 正如我们在讨论的那样，内部使用哈希表实现的无序容器。 通过哈希函数计算的每个项目，以映射到 。 主要优点是，如果我们具有有效的哈希函数，我们可以在O(1)时间中找到元素。 平均而言，它可以达到线性时间。 简而言之，我们可以说它基于所使用的哈希函数的类型。

So we can say these are fastest among all containers.

因此，可以说这些是所有容器中最快的。

As name says that in unordered_set the order is not defined. Unordered set doesn’t allow duplicates.

顾名思义，在unordered_set中未定义顺序。 无序集不允许重复。

C ++ STL无序集– std :: unordered_set (C++ STL Unordered Set – std::unordered_set)

Useful iterators to work on this unordered set:

在此无序集合上工作的有用的迭代器：

begin(): returns iterator to the beginning

begin()：将迭代器返回到开头

end(): returns iterator to the end of the list

end()：将迭代器返回到列表的末尾

cbegin(): returns constant iterator to the beginning

cbegin()：将常量迭代器返回到开头

cend(): returns constant iterator to the end.

cend()：将常量迭代器返回到末尾。

First we need to include unordered_set header file. Which is #include<unordered_set>

首先，我们需要包含unordered_set头文件。 这是#include <unordered_set>

Inserting element into unordered_set:

将元素插入到unordered_set中：

There are various ways to insert elements into unordered_set.

有多种将元素插入unordered_set的方法。

Method 1: Insert directly by passing element.

方法1：通过传递元素直接插入。

UnOrdSet.insert(element);

UnOrdSet.insert(element);

Method 2: Using iterator. This returns iterator at inserted position.

方法2：使用迭代器。 这将在插入位置返回迭代器。

UnOrdSet.insert ( iterator, value)

UnOrdSet.insert(迭代器，值)

Method 3: Copying from another container.

方法3：从另一个容器复制。

Example program to insert into unordered_set:

插入unordered_set的示例程序：

#include
    
     #include 
     
       using namespace std; int main(){	unordered_set
      
        s1; // declaring unordered_set	unordered_set
       
         :: iterator it; // iterator for unordered_set		for(int i=0;i<5;i++){		s1.insert(i*10); // inserting using Method1	}		it= s1.begin();	s1.insert(it,99);		int ary[]= { 23, 34, 45, 56};	s1.insert(ary, ary+4); // Inserting using method3		//checking by printing	for(it= s1.begin(); it!=s1.end(); it++) cout << *it << " ";		// We can observe that output will be print in sorted order. That is the property of Unordered_set		return 0;}
       
      
     
    

Output

输出量

56 45 34 23 40 99 0 10 20 30

56 45 34 23 40 99 0 10 20 30

Modifiers: The functions which effect size/data of that container

修饰符：影响该容器大小/数据的函数

erase(): We can erase an element by specifying value or pointing to iterator.

delete()：我们可以通过指定值或指向迭代器来擦除元素。

swap(): swaps elements of Unordered_set1 to Unorderedset2 and Unorderedset2 to Unordered_set1.

swap()：将 Unordered_set1的元素交换为Unorderedset2，将Unorderedset2的元素交换为Unordered_set1。

clear(): removes all elements in the list. It results list of size 0.

clear()：删除列表中的所有元素。 结果列表大小为0。

Example program to show above functions:

显示上述功能的示例程序：

#include
    
     #include
     
       using namespace std; int main(){	unordered_set
      
        s1;	unordered_set
       
         :: iterator it;		for(int i=0; i<5; i++) s1.insert(i+10);	s1.erase(12); // deleting element 12	cout << "elements after deleting  12 -->";	for(it= s1.begin(); it!=s1.end(); it++) cout << *it << " ";	cout << endl;		unordered_set
        
          s2;	for(int i=0;i<4;i++) s2.insert(i);		cout << "unordered_set 1 elements before swapping -->";	for(it= s1.begin(); it!= s1.end(); it++) cout<< *it << " ";	cout << endl;		cout << "unordered_set 2 elements before swapping -->";	for(it= s2.begin(); it!= s2.end(); it++) cout<< *it << " ";	cout << endl;		s1.swap(s2); // swapping operation 	cout << "unordered_set 1 elements after swapping -->";	for(it= s1.begin(); it!= s1.end(); it++) cout<< *it << " ";	cout << endl;		cout << "unordered_set 2 elements after swapping -->";	for(it= s2.begin(); it!= s2.end(); it++) cout<< *it << " ";	cout << endl; 	s1.clear(); // clearing list 1	cout << "Performing clear() operation on unordered_set1......" << endl;	s1.empty() ? cout <<"Unordered_set is empty" << endl: cout << "unordered_set is not empty" << endl; //	// ternary operation which resutls list is empty or not		return 0;}
        
       
      
     
    

Output

输出量

elements after deleting 12 –>14 10 11 13 unordered_set 1 elements before swapping –>14 10 11 13 unordered_set 2 elements before swapping –>3 2 1 0 unordered_set 1 elements after swapping –>3 2 1 0 unordered_set 2 elements after swapping –>14 10 11 13 Performing clear() operation on unordered_set1…… Unordered_set is empty

删除后的元素12 –> 14 10 11 13 交换前的unordered_set 1个元素–> 14 10 11 13 交换前的2个元素–> 3 2 1 0 交换后的unordered_set 1个元素–> 3 2 1 0 交换后的unordered_set 2个元素–> 14 10 11 13 在unordered_set1上执行clear()操作…… Unordered_set为空

Information retrieving functions:

信息检索功能：

empty(): returns a Boolean value whether Unordered_set is empty or not.

empty()：无论Unordered_set是否为空，都返回一个布尔值。

size(): returns the size of the Unordered_set.

size()：返回Unordered_set的大小。

max_size(): returns the maximum size a Unordered_set can have.

max_size()：返回Unordered_set可以具有的最大大小。

And some more operations are:

还有更多的操作是：

find(): It returns iterator to the element.

find()：将迭代器返回到元素。

count(x):  Returns how many times elements “x” present in Unordered_set.

count(x)：返回Unordered_set中元素“ x”出现的次数。

Example program to show above functions:

显示上述功能的示例程序：

#include
    
     #include
     
       using namespace std; int main(){	unordered_set
      
        s1;	unordered_set
       
         :: iterator it;		for(int i=0; i<5; i++) s1.insert(i+10);	s1.empty() ? cout <<"Unordered_set is empty" << endl: cout << "unordered_set is not empty" << endl;	cout << "size of the unordered_set is " << s1.size() << endl;	cout << "maximum size of the unordered_set is " << s1.max_size() << endl;	cout << "finding elemnt 12 in unordered_set" << endl;	it= s1.find(12);	cout << *it << endl;		s1.insert(12);	if(s1.count(22)) cout << "number 22 is in the unordered_set " << endl;	else cout << "22 is not in the unordered_set";		return 0;}
       
      
     
    

Output

输出量

unordered_set is not empty size of the unordered_set is 5 maximum size of the unordered_set is 1152921504606846975 finding elemnt 12 in unordered_set 12 22 is not in the unordered_set

unordered_set不为空unordered_set的 大小为5 unordered_set的 最大大小为1152921504606846975 发现unordered_set 12中的 元素 12 不在unordered_set中

翻译自:

stl set是无序的