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Chapter 13 set/ multiset of STL

2022-07-19 09:33:00 【qq_ forty-three million two hundred and five thousand two hundr】

1 set Basic concepts

brief introduction ：

All elements are automatically sorted on insertion

The essence ：

set/multiset Belong to Associative containers , The underlying structure is Binary tree Realization .

set and multiset difference ：

set Duplicate elements are not allowed in the container

multiset Allow duplicate elements in the container

2 set Construction and assignment

Function description ： establish set Containers and assignments

structure ：

set<T> st; // Default constructor ：

set(const set &st); // copy constructor

assignment ：

set& operator=(const set &st); // Overload the equal sign operator

Example ：

#include <set> 
void printSet(set<int> & s) 
{
	for (set<int>::iterator it = s.begin(); it != s.end(); it++) 
	{ 
		cout << *it << " "; 
	}
	cout << endl;
}

// Construction and assignment 
void test01() 
{ 
	set<int> s1; 
	s1.insert(20); 
	s1.insert(10); 
	s1.insert(30); 
	s1.insert(40); 
	printSet(s1); 
	
	// Copy structure  
	set<int>s2(s1);
	printSet(s2);
	
	// assignment 
	set<int>s3; 
	s3 = s2;
	printSet(s3); 
}

int main() 
{
	test01(); 
	return 0; 
}

Output results ：

10 20 30 40
10 20 30 40
10 20 30 40

summary ：

set Container inserts data with insert

set The data inserted by the container will be sorted automatically

3 set Size and swap

Function description ：

Statistics set Container size and swap set Containers

The function prototype ：

size(); // Returns the number of elements in the container

empty(); // Judge whether the container is empty

swap(st); // Swap two collection containers

Example ：

#include <set> 
void printSet(set<int> & s) 
{ 
	for (set<int>::iterator it = s.begin(); it != s.end(); it++) 
	{
		cout << *it << " "; }cout << endl;
}

// size  
void test01()
{ 
	set<int> s1; 
	s1.insert(10); 
	s1.insert(30); 
	s1.insert(20);
	s1.insert(40); 
	if (s1.empty())
	{
		cout << "s1 It's empty " << endl; 
	}
	else 
	{ 
		cout << "s1 Not empty " << endl;
		cout << "s1 The size is ： " << s1.size() << endl; 
	} 
}

// In exchange for  
void test02() 
{ 
	set<int> s1; 
	s1.insert(10); 
	s1.insert(30); 
	s1.insert(20); 
	s1.insert(40);
	
	set<int> s2; 
	s2.insert(100); 
	s2.insert(300);
	s2.insert(200); 
	s2.insert(400); 
	
	cout << " Exchange before " << endl; 
	printSet(s1); 
	printSet(s2); 
	cout << endl;
	
	cout << " After exchanging " << endl; 
	s1.swap(s2); 
	printSet(s1); 
	printSet(s2);
}

int main() 
{
	test01(); 
	test02(); 
	return 0; 
}

Output results ：

s1 Not empty 
s1 The size is ： 4
 Exchange before 
10 20 30 40
100 200 300 400

 After exchanging 
100 200 300 400
10 20 30 40

summary ：

Count the size --- size

Determine whether it is null --- empty

Exchange containers --- swap

4 set Insert and delete

Function description ：

set Container to insert data and delete data

The function prototype ：

insert(elem); // Insert elements into the container

clear(); // Remove all elements

erase(pos); // Delete pos The element that iterators refer to , Returns the iterator of the next element

erase(beg, end); // Delete range [beg,end) All elements of , Returns the iterator of the next element

erase(elem); // Delete the value in the container as elem The elements of

Example ：

#include <set>
void printSet(set<int> & s)
{ 
	for (set<int>::iterator it = s.begin(); it != s.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;
}

// Insert and delete  
void test01() 
{
	set<int> s1;
	// Insert 
	s1.insert(10); 
	s1.insert(30); 
	s1.insert(20); 
	s1.insert(40);
	printSet(s1);
	
	// Delete 
	s1.erase(s1.begin()); 
	printSet(s1);
	
	s1.erase(30); 
	printSet(s1); 
	
	// Empty  
	s1.erase(s1.begin(), s1.end()); 
	printSet(s1);
	
	s1.clear(); 
	printSet(s1); 
}

int main() 
{
	test01();
	return 0;
}

Output results ：

10 20 30 40
20 30 40
20 40

summary ：

Insert --- insert

Delete --- erase

Empty --- clear

5 set Find and count

Function description ：

Yes set Container to find data and Statistics

The function prototype ：

find(key); // lookup key Whether there is , If exist , Returns the iterator of the element of the key ; If it does not exist , return set.end();

count(key); // Statistics key Number of elements of

Example ：

#include <set>
// Find and count 
void test01()
{ 
	set<int> s1; 
	
	// Insert 
	s1.insert(10);
	s1.insert(30);
	s1.insert(20); 
	s1.insert(40); 
	
	// lookup 
	set<int>::iterator pos = s1.find(30);
	if (pos != s1.end()) 
	{
		cout << " Found the element  ： " << *pos << endl;
	}
	else 
	{
		cout << " Element not found " << endl;
	}
	
	// Statistics 
	int num = s1.count(30); 
	cout << "num = " << num << endl;
}


int main() 
{ 
	test01(); 
	return 0; 
}

Output results ：

 Found the element  ： 30
num = 1

summary ：

lookup --- find （ The return is an iterator ）

Statistics --- count （ about set, The result is 0 perhaps 1）

6 set and multiset difference

Learning goals ：

master set and multiset The difference between

difference ：

set You can't insert duplicate data , and multiset Sure

set When the data is inserted, the insertion result will be returned , Indicates whether the insertion was successful

multiset It doesn't detect data , So you can insert duplicate data

Example ：

#include <set>
//set and multiset difference  
void test01()
{
	set<int> s; 
	pair<set<int>::iterator, bool> ret = s.insert(10); 
	if (ret.second) 
	{
		cout << " The first insertion was successful !" << endl; 
	}
	else 
	{
		cout << " The first insertion failed !" << endl;
	}
	
	ret = s.insert(10); 
	if (ret.second)
	{
		cout << " The second insertion was successful !" << endl; 
	}
	else 
	{ 
		cout << " The second insertion failed !" << endl; 
	}
	
	//multiset 
	
	multiset<int> ms; 
	ms.insert(10);
	ms.insert(10);
	for (multiset<int>::iterator it = ms.begin(); it != ms.end(); it++) 
	{
		cout << *it << " "; 
	}
	cout << endl;
}

int main()
{
	test01(); 
	return 0; 
}

Output results ：

 The first insertion was successful !
 The second insertion failed !
10 10

summary ：

If duplicate data is not allowed, it can be used set

If it's necessary to insert data reuse multiset

7 pair Create for group

Function description ：

Pairs of data , With pairing, you can return two data

Two ways to create ：

pair<type, type> p ( value1, value2 );

pair<type, type> p = make_pair( value1, value2 );

Example ：

#include <string>
// Create for group  
void test01()
{ 
	pair<string, int> p(string("Tom"), 20);
	cout << " full name ： " << p.first << "  Age ： " << p.second << endl; 

	pair<string, int> p2 = make_pair("Jerry", 10);
	cout << " full name ： " << p2.first << "  Age ： " << p2.second << endl; 
}
int main() 
{
	test01(); 
	return 0;
}

Output results ：

 full name ： Tom  Age ： 20
 full name ： Jerry  Age ： 10

summary ：

You can create pairs of groups in both ways , Just remember one

8 set Container sorting

Learning goals ：

set The default collation of containers is from small to large , Learn how to change the sort rules

The main technical points are ：

Using affine function , You can change the sort rules

Example 1 set Store built-in data types

#include <set>
class MyCompare 
{
public: 
	bool operator()(int v1, int v2)const
	{
		return v1 > v2; 
	} 
};
void test01() 
{
	set<int> s1;
	s1.insert(10); 
	s1.insert(40); 
	s1.insert(20); 
	s1.insert(30);
	s1.insert(50); 
	
	// Default from small to large 
	for (set<int>::iterator it = s1.begin(); it != s1.end(); it++) 
	{ 
		cout << *it << " "; 
	}
	cout << endl;
	
	// Specify collation  
	set<int, MyCompare> s2;
	s2.insert(10); 
	s2.insert(40);
	s2.insert(20); 
	s2.insert(30); 
	s2.insert(50); 
	
	for (set<int, MyCompare>::iterator it = s2.begin(); it != s2.end(); it++)
	{ 
		cout << *it << " "; 
	} 
	cout << endl; 
}

int main()
{ 
	test01(); 
	return 0;
}

summary ： Using a functor, you can specify set Sorting rules for containers

Example 2 set Store custom data types

#include <string> 
class Person 
{
public: 
Person(string name, int age)
{
this->m_Name = name; 
this->m_Age = age; 
}
string m_Name; 
int m_Age; 
};

class comparePerson
{
public: 
	bool operator()(const Person& p1, const Person& p2)const
	{ 
		// Sort by age   Descending  
		return p1.m_Age > p2.m_Age; 
	} 
};

void test01()
{ 
	set<Person, comparePerson> s; 
	Person p1(" Liu bei ", 23);
	Person p2(" Guan yu ", 27); 
	Person p3(" Zhang Fei ", 25); 
	Person p4(" zhaoyun ", 21);
	s.insert(p1); 
	s.insert(p2); 
	s.insert(p3); 
	s.insert(p4); 
	for (set<Person, comparePerson>::iterator it = s.begin(); it != s.end(); it++) 
	{ 
		cout << " full name ： " << it->m_Name << "  Age ： " << it->m_Age << endl;
	}
}

int main()
{
	test01();
	return 0;
}

Output results ：

 full name ：  Guan yu   Age ： 27
 full name ：  Zhang Fei   Age ： 25
 full name ：  Liu bei   Age ： 23
 full name ：  zhaoyun   Age ： 21

summary ：

For custom data types ,set You must specify a collation to insert data

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当前位置：网站首页>Chapter 13 set/ multiset of STL

Chapter 13 set/ multiset of STL

1 set Basic concepts

2 set Construction and assignment

3 set Size and swap

4 set Insert and delete

5 set Find and count

6 set and multiset difference

7 pair Create for group

8 set Container sorting

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