stl set是无序的_C ++ STL无序集– std :: unordered_set

r囧r小猫 2022-12-07 13:52 185阅读 0赞

![bd904544c3143b8672bfb6b74dd2f779.png][]

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 [introduction to stl article][], unordered containers internally implemented with hash tables. Each item calculated by hash function, to map to [hash table][]. 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[stl文章的介绍中][introduction to stl article]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[哈希表][hash table] 。 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);**

**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<iostream>
    #include <unordered_set>
     
    using namespace std;
     
    int main(){
    	unordered_set<int> s1; // declaring unordered_set
    	unordered_set<int> :: 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*

**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<iostream>
    #include<unordered_set>
     
    using namespace std;
     
    int main(){
    	unordered_set<int> s1;
    	unordered_set<int> :: 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<int> 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<iostream>
    #include<unordered_set>
     
    using namespace std;
     
    int main(){
    	unordered_set<int> s1;
    	unordered_set<int> :: 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: [https://www.thecrazyprogrammer.com/2017/10/stl-unordered-set.html][https_www.thecrazyprogrammer.com_2017_10_stl-unordered-set.html]

stl set是无序的

[bd904544c3143b8672bfb6b74dd2f779.png]: /images/20221123/745e60707eaf43cdad247085b1767b3e.png
[introduction to stl article]: https://www.thecrazyprogrammer.com/2017/07/c-standard-template-library-stl.html
[hash table]: https://www.thecrazyprogrammer.com/2017/06/hashing.html
[https_www.thecrazyprogrammer.com_2017_10_stl-unordered-set.html]: https://www.thecrazyprogrammer.com/2017/10/stl-unordered-set.html