STL common algorithms:

Write at the beginning: sort out some algorithms commonly used in stl, involving comparison, exchange, search, traversal, replication, modification, etc. It's worth collecting!!

summary:

• The algorithm is mainly composed of header files < algorithm > < functional > < numeric >.
• < algorithm > is the largest of all STL header files, covering comparison, exchange, search, traversal, copy, modification, etc
• < numeric > is very small and only includes a few template functions that perform simple mathematical operations on the sequence
• < functional > defines some template classes to declare function objects.

1. Common traversal algorithms:

Learning objectives:

• Master common traversal algorithms

Algorithm Introduction:

• for_each / / traverse the container
• transform / / transfer container to another container

1.1 for_each

Function Description:

• Implement traversal container

Function prototype:

• for_each(iterator beg, iterator end, _func);

  //The traversal algorithm traverses the container elements

  //beg start iterator

  //End end iterator

  // _ func function or function object

Example:

#include <algorithm>
#include <vector>

//Ordinary function
void print01(int val) 
{
	cout << val << " ";
}
//Function object
class print02 
{
 public:
	void operator()(int val) 
	{
		cout << val << " ";
	}
};

//for_ Basic usage of each algorithm
void test01() 
{

	vector<int> v;
	for (int i = 0; i < 10; i++) 
	{
		v.push_back(i);
	}

	//inorder traversal 
	for_each(v.begin(), v.end(), print01);
	cout << endl;

	for_each(v.begin(), v.end(), print02());
	cout << endl;
}

int main() 
{

	test01();

	system("pause");

	return 0;
}

Summary: for_each is the most commonly used traversal algorithm in practical development, which needs to be mastered

1.2 transform

Function Description:

• Transport container to another container

Function prototype:

• transform(iterator beg1, iterator end1, iterator beg2, _func);

//beg1 source container start iterator

//end1 source container end iterator

//beg2 target container start iterator

//_ func function or function object

Example:

#include<vector>
#include<algorithm>

//Common traversal algorithms

class TransForm
{
public:
	int operator()(int val)
	{
		return val;
	}

};

class MyPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	vector<int>v;
	for (int i = 0; i < 10; i++)
	{
		v.push_back(i);
	}

	vector<int>vTarget; //Target container

	vTarget.resize(v.size()); // The target container needs to open up space in advance

	transform(v.begin(), v.end(), vTarget.begin(), TransForm());

	for_each(vTarget.begin(), vTarget.end(), MyPrint());
}

int main() 
{

	test01();

	system("pause");

	return 0;
}

Conclusion: the target container to be handled must be opened up in advance, otherwise it cannot be handled normally

2. Common search algorithms:

Learning objectives:

• Master common search algorithms

Algorithm Introduction:

• Find / / find elements
• find_if / / find elements by criteria
• adjacent_find / / find adjacent duplicate elements
• binary_search / / binary search
• Count / / count the number of elements
• count_if / / count the number of elements by condition

2.1 find

Function Description:

• Find the specified element, find the iterator that returns the specified element, and cannot find the return end iterator end()

Function prototype:

• find(iterator beg, iterator end, value);

  //Find the element by value, find the iterator that returns the specified position, and the iterator that returns the end position cannot be found

  //beg start iterator

  //End end iterator

  //value lookup element

Example:

#include <algorithm>
#include <vector>
#include <string>
void test01() 
{

	vector<int> v;
	for (int i = 0; i < 10; i++) 
	{
		v.push_back(i + 1);
	}
	//Find out if there is 5 this element in the container
	vector<int>::iterator it = find(v.begin(), v.end(), 5);
	if (it == v.end()) 
	{
		cout << "Can't find!" << endl;
	}
	else 
	{
		cout << "find:" << *it << endl;
	}
}

class Person 
{
public:
	Person(string name, int age) 
	{
		this->m_Name = name;
		this->m_Age = age;
	}
	//Heavy load==
	bool operator==(const Person& p) 
	{
		if (this->m_Name == p.m_Name && this->m_Age == p.m_Age) 
		{
			return true;
		}
		return false;
	}

public:
	string m_Name;
	int m_Age;
};

void test02() 
{

	vector<Person> v;

	//Create data
	Person p1("aaa", 10);
	Person p2("bbb", 20);
	Person p3("ccc", 30);
	Person p4("ddd", 40);

	v.push_back(p1);
	v.push_back(p2);
	v.push_back(p3);
	v.push_back(p4);

	vector<Person>::iterator it = find(v.begin(), v.end(), p2);
	if (it == v.end()) 
	{
		cout << "Can't find!" << endl;
	}
	else 
	{
		cout << "Find name:" << it->m_Name << " Age: " << it->m_Age << endl;
	}
}

Summary: find can find the specified element in the container, and the return value is the iterator

2.2 find_if

Function Description:

• Find elements by criteria

Function prototype:

• find_if(iterator beg, iterator end, _Pred);

  //Find the element by value, find the iterator that returns the specified position, and the iterator that returns the end position cannot be found

  //beg start iterator

  //End end iterator

  // _ Pred function or predicate (returns an imitation function of bool type)

Example:

#include <algorithm>
#include <vector>
#include <string>

//Built in data type
class GreaterFive
{
public:
	bool operator()(int val)
	{
		return val > 5;
	}
};

void test01() 
{
	vector<int> v;
	for (int i = 0; i < 10; i++) 
	{
		v.push_back(i + 1);
	}

	vector<int>::iterator it = find_if(v.begin(), v.end(), GreaterFive());
	if (it == v.end()) 
	{
		cout << "Can't find!" << endl;
	}
	else 
	{
		cout << "A number greater than 5 was found:" << *it << endl;
	}
}

//Custom data type
class Person 
{
public:
	Person(string name, int age)
	{
		this->m_Name = name;
		this->m_Age = age;
	}
public:
	string m_Name;
	int m_Age;
};

class Greater20
{
public:
	bool operator()(Person &p)
	{
		return p.m_Age > 20;
	}

};

void test02() 
{
	vector<Person> v;

	//Create data
	Person p1("aaa", 10);
	Person p2("bbb", 20);
	Person p3("ccc", 30);
	Person p4("ddd", 40);

	v.push_back(p1);
	v.push_back(p2);
	v.push_back(p3);
	v.push_back(p4);

	vector<Person>::iterator it = find_if(v.begin(), v.end(), Greater20());
	if (it == v.end())
	{
		cout << "Can't find!" << endl;
	}
	else
	{
		cout << "Find name:" << it->m_Name << " Age: " << it->m_Age << endl;
	}
}

int main() 
{
	//test01();

	test02();

	system("pause");

	return 0;
}

Summary: find_if search by condition makes the search more flexible, and the provided imitation function can change different strategies

2.3 adjacent_find

Function Description:

• Find adjacent duplicate elements

Function prototype:

• adjacent_find(iterator beg, iterator end);

  //Find adjacent repeating elements and return the iterator at the first position of adjacent elements

  //beg start iterator

  //End end iterator

Example:

#include <algorithm>
#include <vector>

void test01()
{
	vector<int> v;
	v.push_back(1);
	v.push_back(2);
	v.push_back(5);
	v.push_back(2);
	v.push_back(4);
	v.push_back(4);
	v.push_back(3);

	//Find adjacent duplicate elements
	vector<int>::iterator it = adjacent_find(v.begin(), v.end());
	if (it == v.end()) 
	{
		cout << "can't find!" << endl;
	}
	else 
	{
		cout << "The adjacent duplicate element found is:" << *it << endl;
	}
}

Summary: if you find adjacent repeating elements in an interview question, remember to use the adjacent in STL_ Find algorithm

2.4 binary_search

Function Description:

• Finds whether the specified element exists

Function prototype:

• bool binary_search(iterator beg, iterator end, value);

  //Find the specified element and return true, otherwise false

  //Note: not available in unordered sequences

  //beg start iterator

  //End end iterator

  //value lookup element

Example:

#include <algorithm>
#include <vector>

void test01()
{
	vector<int>v;

	for (int i = 0; i < 10; i++)
	{
		v.push_back(i);
	}
	//Binary search
	bool ret = binary_search(v.begin(), v.end(),2);
	if (ret)
	{
		cout << "eureka" << endl;
	}
	else
	{
		cout << "not found" << endl;
	}
}

int main() 
{

	test01();

	system("pause");

	return 0;
}

Summary: the binary search method is very efficient. It is worth noting that the elements in the container must be in an orderly sequence

2.5 count

Function Description:

• Number of statistical elements

Function prototype:

• count(iterator beg, iterator end, value);

  //Count the number of occurrences of the element

  //beg start iterator

  //End end iterator

  //Element of value statistics

Example:

#include <algorithm>
#include <vector>

//Built in data type
void test01()
{
	vector<int> v;
	v.push_back(1);
	v.push_back(2);
	v.push_back(4);
	v.push_back(5);
	v.push_back(3);
	v.push_back(4);
	v.push_back(4);

	int num = count(v.begin(), v.end(), 4);

	cout << "4 The number of is: " << num << endl;
}

//Custom data type
class Person
{
public:
	Person(string name, int age)
	{
		this->m_Name = name;
		this->m_Age = age;
	}
	bool operator==(const Person & p)
	{
		if (this->m_Age == p.m_Age)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
	string m_Name;
	int m_Age;
};

void test02()
{
	vector<Person> v;

	Person p1("wy", 33);
	Person p2("cdc", 32);
	Person p3("hw", 44);
	Person p4("lzh", 19);
	Person p5("yt", 25);

	v.push_back(p1);
	v.push_back(p2);
	v.push_back(p3);
	v.push_back(p4);
	v.push_back(p5);
    
    Person p("zh",35);

	int num = count(v.begin(), v.end(), p);
	cout << "num = " << num << endl;
}
int main() 
{

	//test01();

	test02();

	system("pause");

	return 0;
}

Summary: when counting user-defined data types, it is necessary to overload the operator==

2.6 count_if

Function Description:

• Count the number of elements by condition

Function prototype:

• count_if(iterator beg, iterator end, _Pred);

  //Count the occurrence times of elements by conditions

  //beg start iterator

  //End end iterator

  // _ Pred predicate

Example:

#include <algorithm>
#include <vector>

class Greater4
{
public:
	bool operator()(int val)
	{
		return val >= 4;
	}
};

//Built in data type
void test01()
{
	vector<int> v;
	v.push_back(1);
	v.push_back(2);
	v.push_back(4);
	v.push_back(5);
	v.push_back(3);
	v.push_back(4);
	v.push_back(4);

	int num = count_if(v.begin(), v.end(), Greater4());

	cout << "The number greater than 4 is: " << num << endl;
}

//Custom data type
class Person
{
public:
	Person(string name, int age)
	{
		this->m_Name = name;
		this->m_Age = age;
	}

	string m_Name;
	int m_Age;
};

class AgeLess35
{
public:
	bool operator()(const Person &p)
	{
		return p.m_Age < 35;
	}
};
void test02()
{
	vector<Person> v;

	Person p1("Wang Yuan", 35);
	Person p2("Juen-Kai Wang", 35);
	Person p3("Jackson Yee", 35);
	Person p4("Xiao Zhan", 30);
	Person p5("Fan Ye", 25);

	v.push_back(p1);
	v.push_back(p2);
	v.push_back(p3);
	v.push_back(p4);
	v.push_back(p5);

	int num = count_if(v.begin(), v.end(), AgeLess35());
	cout << "Number of children under 35 years old:" << num << endl;
}


int main() 
{

	//test01();

	test02();

	system("pause");

	return 0;
}

Summary: count is used for statistics by value and count is used for statistics by condition_ if

3. Common sorting algorithms:

Learning objectives:

• Master common sorting algorithms

Algorithm Introduction:

• Sort / / sort the elements in the container
• random_shuffle / / shuffle the elements within the specified range to randomly adjust the order
• Merge / / merge container elements and store them in another container
• reverse / / reverses the elements of the specified range

3.1 sort

Function Description:

• Sort the elements in the container

Function prototype:

• sort(iterator beg, iterator end, _Pred);

  //Find the element by value, find the iterator that returns the specified position, and the iterator that returns the end position cannot be found

  //beg start iterator

  //End end iterator

  // _ Pred predicate

Example:

#include <algorithm>
#include <vector>

void myPrint(int val)
{
	cout << val << " ";
}

void test01() 
{
	vector<int> v;
	v.push_back(10);
	v.push_back(30);
	v.push_back(50);
	v.push_back(20);
	v.push_back(40);

	//sort sorts from small to large by default
	sort(v.begin(), v.end());
	for_each(v.begin(), v.end(), myPrint);
	cout << endl;

	//Sort from large to small
	sort(v.begin(), v.end(), greater<int>());
	for_each(v.begin(), v.end(), myPrint);
	cout << endl;
}

int main() 
{

	test01();

	system("pause");

	return 0;
}

Summary: sort is one of the most commonly used algorithms in development and needs to be mastered

3.2 random_shuffle

Function Description:

• Shuffle the elements in the specified range to adjust the order randomly

Function prototype:

• random_shuffle(iterator beg, iterator end);

  //Randomly adjust the order of elements within the specified range

  //beg start iterator

  //End end iterator

Example:

#include <algorithm>
#include <vector>
#include <ctime>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	srand((unsigned int)time(NULL));
	vector<int> v;
	for(int i = 0 ; i < 10;i++)
	{
		v.push_back(i);
	}
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;

	//Disorder order
	random_shuffle(v.begin(), v.end());
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary: random_shuffle shuffle algorithm is more practical. Remember to add random number seeds when using it

3.3 merge

Function Description:

• The two container elements are merged and stored in another container

Function prototype:

• merge(iterator beg1, iterator end1, iterator beg2, iterator end2, iterator dest);

  //Container elements are merged and stored in another container

  //Note: the two containers must be ordered

  //beg1 container 1 start iterator
  //end1 container 1 end iterator
  //beg2 container 2 start iterator
  //end2 container 2 end iterator
  //dest destination container start iterator

Example:

#include <algorithm>
#include <vector>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	vector<int> v1;
	vector<int> v2;
	for (int i = 0; i < 10 ; i++) 
    {
		v1.push_back(i);
		v2.push_back(i + 1);
	}

	vector<int> vtarget;
	//The target container needs to open up space in advance
	vtarget.resize(v1.size() + v2.size());
	//Merging requires two ordered sequences
	merge(v1.begin(), v1.end(), v2.begin(), v2.end(), vtarget.begin());
	for_each(vtarget.begin(), vtarget.end(), myPrint());
	cout << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary: the two containers merged by the merge must have an ordered sequence

3.4 reverse

Function Description:

• Invert the elements in the container

Function prototype:

• reverse(iterator beg, iterator end);

  //Inverts the elements of the specified range

  //beg start iterator

  //End end iterator

Example:

#include <algorithm>
#include <vector>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	vector<int> v;
	v.push_back(10);
	v.push_back(30);
	v.push_back(50);
	v.push_back(20);
	v.push_back(40);

	cout << "Before reversing: " << endl;
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;

	cout << "After reversal: " << endl;

	reverse(v.begin(), v.end());
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary: reverse reverses the elements in the interval, which may be involved in the interview question

4. Common copy and replacement algorithms:

Learning objectives:

• Master common copy and replacement algorithms

Algorithm Introduction:

• Copy / / copy the elements of the specified range in the container to another container
• replace / / modify the old element of the specified range in the container to a new element
• replace_if / / replace the qualified element in the specified range in the container with a new element
• Swap / / swap elements of two containers

4.1 copy

Function Description:

• Copies the specified range of elements in a container to another container

Function prototype:

• copy(iterator beg, iterator end, iterator dest);

  //Find the element by value, find the iterator that returns the specified position, and the iterator that returns the end position cannot be found

  //beg start iterator

  //End end iterator

  //dest target start iterator

Example:

#include <algorithm>
#include <vector>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	vector<int> v1;
	for (int i = 0; i < 10; i++) 
	{
		v1.push_back(i + 1);
	}
	vector<int> v2;
	v2.resize(v1.size());
	copy(v1.begin(), v1.end(), v2.begin());

	for_each(v2.begin(), v2.end(), myPrint());
	cout << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary: when using copy algorithm to copy, the target container should remember to open up space in advance

4.2 replace

Function Description:

• Modifies the old element of the specified range in the container to a new element

Function prototype:

• replace(iterator beg, iterator end, oldvalue, newvalue);

  //Replace the old element in the interval with a new element

  //beg start iterator

  //End end iterator

  //oldvalue old element

  //newvalue new element

Example:

#include <algorithm>
#include <vector>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	vector<int> v;
	v.push_back(20);
	v.push_back(30);
	v.push_back(20);
	v.push_back(40);
	v.push_back(50);
	v.push_back(10);
	v.push_back(20);

	cout << "Before replacement:" << endl;
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;

	//Replace 20 in the container with 2000
	cout << "After replacement:" << endl;
	replace(v.begin(), v.end(), 20,2000);
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary: replace will replace the qualified elements in the interval

4.3 replace_if

Function Description:

• Replace the qualified elements in the interval with the specified elements

Function prototype:

• replace_if(iterator beg, iterator end, _pred, newvalue);

  //Replace the element according to the condition, and replace the qualified element with the specified element

  //beg start iterator

  //End end iterator

  // _ pred predicate

  //New element replaced by newvalue

Example:

#include <algorithm>
#include <vector>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

class ReplaceGreater30
{
public:
	bool operator()(int val)
	{
		return val >= 30;
	}

};

void test01()
{
	vector<int> v;
	v.push_back(20);
	v.push_back(30);
	v.push_back(20);
	v.push_back(40);
	v.push_back(50);
	v.push_back(10);
	v.push_back(20);

	cout << "Before replacement:" << endl;
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;

	//Replace 30 or more in the container with 3000
	cout << "After replacement:" << endl;
	replace_if(v.begin(), v.end(), ReplaceGreater30(), 3000);
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary: replace_if search by condition, you can use the imitation function to flexibly filter the satisfied conditions

4.4 swap

Function Description:

• Swap elements of two containers

Function prototype:

• swap(container c1, container c2);

  //Swap elements of two containers

  //c1 container 1

  //c2 container 2

Example:

#include <algorithm>
#include <vector>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	vector<int> v1;
	vector<int> v2;
	for (int i = 0; i < 10; i++) 
	{
		v1.push_back(i);
		v2.push_back(i+100);
	}

	cout << "Before exchange: " << endl;
	for_each(v1.begin(), v1.end(), myPrint());
	cout << endl;
	for_each(v2.begin(), v2.end(), myPrint());
	cout << endl;

	cout << "After exchange: " << endl;
	swap(v1, v2);
	for_each(v1.begin(), v1.end(), myPrint());
	cout << endl;
	for_each(v2.begin(), v2.end(), myPrint());
	cout << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary: when swap containers, pay attention to the same type of containers to be exchanged

5. Common arithmetic generation algorithms:

Learning objectives:

• Master common arithmetic generation algorithms

be careful:

• The arithmetic generation algorithm belongs to a small algorithm. When used, the header file included is #include < numeric >

Algorithm Introduction:

• Calculate / / calculate the cumulative sum of container elements

• fill / / add element to container

5.1 accumulate

Function Description:

• Calculate the cumulative sum of interval content container elements

Function prototype:

• accumulate(iterator beg, iterator end, value);

  //Calculate cumulative sum of container elements

  //beg start iterator

  //End end iterator

  //Value starting value

Example:

#include <numeric>
#include <vector>
void test01()
{
	vector<int> v;
	for (int i = 0; i <= 100; i++) 
	{
		v.push_back(i);
	}

	int total = accumulate(v.begin(), v.end(), 0);

	cout << "total = " << total << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary: when using accumulate, the header file should be numeric. This algorithm is very practical

5.2 fill

Function Description:

• Fills the container with the specified element

Function prototype:

• fill(iterator beg, iterator end, value);

  //Fill the container with elements

  //beg start iterator

  //End end iterator

  //Value padded value

Example:

#include <numeric>
#include <vector>
#include <algorithm>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{

	vector<int> v;
	v.resize(10);
	//fill
	fill(v.begin(), v.end(), 100);

	for_each(v.begin(), v.end(), myPrint());
	cout << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary: fill can be used to fill the elements in the container interval with the specified value

6. Common set algorithms

Learning objectives:

• Master common set algorithms

Algorithm Introduction:

• set_intersection / / find the intersection of two containers

• set_union / / find the union of two containers

• set_difference / / find the difference between two containers

6.1 set_intersection

Function Description:

• Find the intersection of two containers

Function prototype:

• set_intersection(iterator beg1, iterator end1, iterator beg2, iterator end2, iterator dest);

  //Find the intersection of two sets

  //Note: the two sets must be an ordered sequence

  //beg1 container 1 start iterator
  //end1 container 1 end iterator
  //beg2 container 2 start iterator
  //end2 container 2 end iterator
  //dest destination container start iterator

Example:

#include <vector>
#include <algorithm>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	vector<int> v1;
	vector<int> v2;
	for (int i = 0; i < 10; i++)
    {
		v1.push_back(i);
		v2.push_back(i+5);
	}

	vector<int> vTarget;
	//Take the smaller of the two values to make room for the target container
	vTarget.resize(min(v1.size(), v2.size()));

	//Returns the iterator address of the last element of the destination container
	vector<int>::iterator itEnd = 
        set_intersection(v1.begin(), v1.end(), v2.begin(), v2.end(), vTarget.begin());
        
	for_each(vTarget.begin(), itEnd, myPrint());
	cout << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary:

• Find the ordered sequence of two sets of intersection
• The target container needs to take a small value from the two containers to open up space
• set_ The return value of intersection is the position of the last element in the intersection

6.2 set_union

Function Description:

• Find the union of two sets

Function prototype:

• set_union(iterator beg1, iterator end1, iterator beg2, iterator end2, iterator dest);

  //Find the union of two sets

  //Note: the two sets must be an ordered sequence

  //beg1 container 1 start iterator
  //end1 container 1 end iterator
  //beg2 container 2 start iterator
  //end2 container 2 end iterator
  //dest destination container start iterator

Example:

#include <vector>
#include <algorithm>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	vector<int> v1;
	vector<int> v2;
	for (int i = 0; i < 10; i++) 
	{
		v1.push_back(i);
		v2.push_back(i+5);
	}

	vector<int> vTarget;
	//Take the sum of the two containers to make room for the target container
	vTarget.resize(v1.size() + v2.size());

	//Returns the iterator address of the last element of the destination container
	vector<int>::iterator itEnd = 
        set_union(v1.begin(), v1.end(), v2.begin(), v2.end(), vTarget.begin());

	for_each(vTarget.begin(), itEnd, myPrint());
	cout << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary:

• An ordered sequence of two sets of union sets
• The target container needs to add two containers to open up space
• set_ The union return value is the position of the last element in the union set

6.3 set_difference

Function Description:

• Find the difference set of two sets

Function prototype:

• set_difference(iterator beg1, iterator end1, iterator beg2, iterator end2, iterator dest);

  //Find the difference set of two sets

  //Note: the two sets must be an ordered sequence

  //beg1 container 1 start iterator
  //end1 container 1 end iterator
  //beg2 container 2 start iterator
  //end2 container 2 end iterator
  //dest destination container start iterator

Example:

#include <vector>
#include <algorithm>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	vector<int> v1;
	vector<int> v2;
	for (int i = 0; i < 10; i++) 
	{
		v1.push_back(i);
		v2.push_back(i+5);
	}

	vector<int> vTarget;
	//Take the larger of the two values to make room for the target container
	vTarget.resize( max(v1.size() , v2.size()));

	//Returns the iterator address of the last element of the destination container
	cout << "v1 And v2 The difference set of is: " << endl;
	vector<int>::iterator itEnd = 
        set_difference(v1.begin(), v1.end(), v2.begin(), v2.end(), vTarget.begin());
	for_each(vTarget.begin(), itEnd, myPrint());
	cout << endl;


	cout << "v2 And v1 The difference set of is: " << endl;
	itEnd = set_difference(v2.begin(), v2.end(), v1.begin(), v1.end(), vTarget.begin());
	for_each(vTarget.begin(), itEnd, myPrint());
	cout << endl;
}

int main() 
{
	test01();

	system("pause");

	return 0;
}

Summary:

• The two sets of difference sets must be ordered sequences
• The target container needs to take a larger value from two containers to open up space
• set_ The return value of difference is the position of the last element in the difference set

Write at the end:

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