Wiki

Common Algorithms

Updated 2023-10-05About 27 min read

Existing English translations were reused. 14 current source blocks remain in Simplified Chinese, without triggering paid translation.

1.STL- Common Algorithms

Overview:

The algorithm is mainly composed of the header files<algorithm> <functional> <numeric>composition.
<algorithm>It is the largest of all STL header files, covering comparison, swapping, searching, traversal operations, copying, modification, and so on.
<numeric>It is very small and includes only a few template functions that perform simple mathematical operations on sequences.
<functional>It defines some template classes used to declare function objects.

1.1.常用范围限制算法

1.1.1.std::clamp（C++17）

Function description:

把一个值限制在闭区间 [下限, 上限] 内，也叫“限幅”或“钳位”。
小于下限时返回下限，大于上限时返回上限，在区间内时返回原值。
属于标准库的 STL 算法，定义在 <algorithm> 中，C++17 起支持。

Function prototype:

template<class T>
constexpr const T& clamp(const T& v, const T& lo, const T& hi);

日常使用时写成 std::clamp(值, 下限, 上限) 即可。它返回限制后的结果，不会直接修改传入的变量；要更新原变量，需要接收返回值。

调用	返回值	原因
`std::clamp(-5, 0, 10)`	`0`	小于下限
`std::clamp(0, 0, 10)`	`0`	等于下限
`std::clamp(6, 0, 10)`	`6`	位于区间内
`std::clamp(10, 0, 10)`	`10`	等于上限
`std::clamp(15, 0, 10)`	`10`	大于上限

Example:

下面先观察不同输入的返回值，再把速度指令限制在 [-2.0, 2.0] 内。

#include <algorithm>
#include <initializer_list>
#include <iostream>

int main()
{
    for (int value : {-5, 0, 6, 10, 15})
    {
        int limited = std::clamp(value, 0, 10);
        std::cout << value << " -> " << limited << '\n';
    }

    double speed = 3.5;
    double limitedSpeed = std::clamp(speed, -2.0, 2.0);
    std::cout << "original speed: " << speed << '\n';
    std::cout << "limited speed: " << limitedSpeed << '\n';

    // 需要修改原变量时，把结果赋值回去。
    speed = std::clamp(speed, -2.0, 2.0);
    std::cout << "updated speed: " << speed << '\n';
    return 0;
}

Operation result:

-5 -> 0
0 -> 0
6 -> 6
10 -> 10
15 -> 10
original speed: 3.5
limited speed: 2
updated speed: 2

使用 GCC 或 Clang 时，编译示例需要启用 C++17 或更高标准，例如 g++ -std=c++17 main.cpp -o main。

常见错误：

上下限写反：默认比较方式要求 lo <= hi。例如 std::clamp(5, 10, 0) 不会自动交换上下限，这样写会产生未定义行为。
参数类型不一致：直接调用时，三个参数应使用相同类型。例如 double speed = 3.5; 应写 std::clamp(speed, -2.0, 2.0)，写成 std::clamp(speed, -2, 2) 会导致模板类型推导失败。
用引用接收临时量：返回类型是 const T&，结果可能引用输入值或某个边界。如果边界是临时量，例如 const auto& result = std::clamp(15, 0, 10);，语句结束后引用会悬空。日常保存数值结果时，使用 auto result = std::clamp(15, 0, 10); 按值接收即可。
把它当作非法输入检查：限幅会直接把越界值变成边界值。如果业务要求拒绝非法输入，应先判断范围；浮点数还应按业务需要检查 NaN，不能指望 clamp 自动处理。

总结：std::clamp 适合速度、音量、亮度等有明确上下限的数值。它既属于 STL 算法，也属于 C++17 引入的现代 C++ 标准库工具。

参考：C++ 标准草案中的 clamp 定义。

1.2.Common traversal algorithms

Learning Objectives:

Master commonly used traversal algorithms

Algorithm Introduction:

for_each //Traverse the container
transform //Move the container to another container

1.2.1.for_each

Function description:

Implement container traversal

Function prototype:

for_each(iterator beg, iterator end, _func);

// Traversal algorithm: traverse container elements

// beg start iterator

// end end iterator

// _func function or function object

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

//普通函数
void print01(int val) 
{
	cout << val << " ";
}
//函数对象
class print02 
{
 public:
	void operator()(int val) 
	{
		cout << val << " ";
	}
};

//for_each算法基本用法
void test01() {

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

	//遍历算法
	for_each(v.begin(), v.end(), print01);
	cout << endl;

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

int main() {

	test01();


	return 0;
}

Operation result:

0 1 2 3 4 5 6 7 8 9
0 1 2 3 4 5 6 7 8 9

**Summary:** for_each is the most commonly used traversal algorithm in practical development and must be mastered proficiently.

1.2.2.transform

Function description:

Move the container into another container

Function prototype:

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

//beg1 Source container begin iterator

//end1 Source container end iterator

//beg2 Iterator to the beginning of the target container

//_func Function or function object

Example:

#include <iostream>
#include<vector>
#include<algorithm>

using namespace std;

//常用遍历算法  搬运 transform

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; //目标容器

	vTarget.resize(v.size()); // 目标容器需要提前开辟空间

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

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

int main() {

	test01();


	return 0;
}

Operation result:

0 1 2 3 4 5 6 7 8 9

Summary: The target container for handling must have space allocated in advance; otherwise, handling cannot proceed normally.

1.3.Common Search Algorithms

Learning objectives:

Master commonly used search algorithms

Algorithm Introduction:

find //Find element
find_if //Find element by condition
adjacent_find //Find adjacent duplicate elements
binary_search //Binary search method
count //Count the number of elements
count_if //Count the number of elements by condition

1.3.1.find

Function description:

Find the specified element; if found, return an iterator to the specified element; if not found, return the end iterator end().

Function prototype:

find(iterator beg, iterator end, value);

// Find an element by value; if found, return an iterator to the specified position; if not found, return the end iterator position

// beg is the starting iterator

// end is the ending iterator

// value is the element to find

Example:

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

using namespace std;

void test01() {

	vector<int> v;
	for (int i = 0; i < 10; i++) {
		v.push_back(i + 1);
	}
	//查找容器中是否有 5 这个元素
	vector<int>::iterator it = find(v.begin(), v.end(), 5);
	if (it == v.end()) 
	{
		cout << "没有找到!" << endl;
	}
	else 
	{
		cout << "找到:" << *it << endl;
	}
}

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

	//创建数据
	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 << "没有找到!" << endl;
	}
	else 
	{
		cout << "找到姓名:" << it->m_Name << " 年龄: " << it->m_Age << endl;
	}
}

Run result: This code block does not contain the main function; it is a syntax, interface, or multi-file example and cannot be run independently, so there is no terminal output.

Summary: Use find to locate a specified element in a container; the return value is aniterator

1.3.2.find_if

Function description:

Find elements by condition

Function prototype:

find_if(iterator beg, iterator end, _Pred);

// Find element by value; if found, return an iterator to the specified position; if not found, return the end iterator

// beg: begin iterator

// end: end iterator

// _Pred: function or predicate (a functor that returns bool)

Example:

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

using namespace std;

//内置数据类型
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 << "没有找到!" << endl;
	}
	else {
		cout << "找到大于5的数字:" << *it << endl;
	}
}

//自定义数据类型
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;

	//创建数据
	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 << "没有找到!" << endl;
	}
	else
	{
		cout << "找到姓名:" << it->m_Name << " 年龄: " << it->m_Age << endl;
	}
}

int main() {

	//test01();

	test02();


	return 0;
}

Operation result:

找到姓名:ccc 年龄: 30

Summary: find_if Conditional lookup makes searching more flexible, and the provided functors can change different strategies

1.3.3.adjacent_find

Function description:

Find adjacent duplicate elements

Function prototype:

adjacent_find(iterator beg, iterator end);

// Find adjacent duplicate elements, returns an iterator to the first position of the adjacent elements

// beg Start iterator

// end End iterator

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

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);

	//查找相邻重复元素
	vector<int>::iterator it = adjacent_find(v.begin(), v.end());
	if (it == v.end()) {
		cout << "找不到!" << endl;
	}
	else {
		cout << "找到相邻重复元素为:" << *it << endl;
	}
}

Run result: This code block does not contain the main function; it is a syntax, interface, or multi-file example and cannot be run independently, so there is no terminal output.

Summary: If a problem in an interview asks you to find adjacent duplicate elements, remember to use the adjacent_find algorithm in the STL.

1.3.4.binary_search

Function description:

Check whether the specified element exists

Function prototype:

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

// Find the specified element, return true if found, otherwise false

// Note: Not available inunordered sequences

// beg Start iterator

// end End iterator

// value The element to find

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

void test01()
{
	vector<int>v;

	for (int i = 0; i < 10; i++)
	{
		v.push_back(i);
	}
	//二分查找
	bool ret = binary_search(v.begin(), v.end(),2);
	if (ret)
	{
		cout << "找到了" << endl;
	}
	else
	{
		cout << "未找到" << endl;
	}
}

int main() {

	test01();


	return 0;
}

Operation result:

找到了

**Summary:** The binary search method has very high search efficiency; it is worth noting that the elements in the container being searched must be in an ordered sequence.

1.3.5.count

Function description:

Count the number of elements

Function prototype:

count(iterator beg, iterator end, value);

// Count the number of occurrences of an element

// beg Start iterator

// end End iterator

// value The element to count

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

//内置数据类型
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的个数为： " << num << endl;
}

//自定义数据类型
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("刘备", 35);
	Person p2("关羽", 35);
	Person p3("张飞", 35);
	Person p4("赵云", 30);
	Person p5("曹操", 25);

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

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

	//test01();

	test02();


	return 0;
}

Operation result:

num = 3

Summary: When counting custom data types, it is necessary to overload operator==

1.3.6.count_if

Function description:

Count elements by condition

Function prototype:

count_if(iterator beg, iterator end, _Pred);

// Count the number of occurrences of elements by condition

// beg Start iterator

// end End iterator

// _Pred Predicate

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

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

//内置数据类型
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 << "大于4的个数为： " << num << endl;
}

//自定义数据类型
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("刘备", 35);
	Person p2("关羽", 35);
	Person p3("张飞", 35);
	Person p4("赵云", 30);
	Person p5("曹操", 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 << "小于35岁的个数：" << num << endl;
}

int main() {

	//test01();

	test02();


	return 0;
}

Operation result:

小于35岁的个数：2

**Summary:** Use count for statistics by value, and use count_if for statistics by condition.

1.4.Common Sorting Algorithms

Learning Objectives:

Master commonly used sorting algorithms

Algorithm Introduction:

sort //Sort elements within the container
random_shuffle //Shuffle randomly reorder elements within the specified range
merge // Merge container elements and store them into another container
reverse // Reverse the elements in the specified range

1.4.1.sort

Function description:

Sort the elements within the container

Function prototype:

sort(iterator beg, iterator end, _Pred);

// Find an element by value; if found, return an iterator to the specified position; if not found, return the end iterator

// beg start iterator

// end end iterator

// _Pred predicate

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

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默认从小到大排序
	sort(v.begin(), v.end());
	for_each(v.begin(), v.end(), myPrint);
	cout << endl;

	//从大到小排序
	sort(v.begin(), v.end(), greater<int>());
	for_each(v.begin(), v.end(), myPrint);
	cout << endl;
}

int main() {

	test01();


	return 0;
}

Operation result:

10 20 30 40 50
50 40 30 20 10

**Summary:** Sorting is one of the most commonly used algorithms in development and must be mastered proficiently.

1.4.2.random_shuffle

Function description:

Shuffle Randomly reorder elements within a specified range

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

using namespace std;

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;

	//打乱顺序
	random_shuffle(v.begin(), v.end());
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;
}

int main() {

	test01();


	return 0;
}

Run results (random numbers may vary with the runtime environment; the following is an example from one run):

0 1 2 3 4 5 6 7 8 9
2 4 5 8 6 0 9 3 7 1

**Summary:**random_shuffle The shuffle algorithm is quite practical; remember to add a random seed when using it.

1.4.3.merge

Function description:

Merge two container elements and store them in another container.

Function prototype:

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

// Merge container elements and store them in another container

// Note: The two containers must beordered

// beg1 Iterator to the beginning of container 1 // end1 Iterator to the end of container 1 // beg2 Iterator to the beginning of container 2 // end2 Iterator to the end of container 2 // dest Iterator to the beginning of the destination container

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

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;
	//目标容器需要提前开辟空间
	vtarget.resize(v1.size() + v2.size());
	//合并  需要两个有序序列
	merge(v1.begin(), v1.end(), v2.begin(), v2.end(), vtarget.begin());
	for_each(vtarget.begin(), vtarget.end(), myPrint());
	cout << endl;
}

int main() {

	test01();


	return 0;
}

Operation result:

0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10

**Summary:** The two containers merged by merge must be ordered sequences.

1.4.4.reverse

Function description:

Reverse the elements in the container

Function prototype:

reverse(iterator beg, iterator end);

// Reverses the elements in the specified range

// beg The beginning iterator

// end The ending iterator

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

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 << "反转前： " << endl;
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;

	cout << "反转后： " << endl;

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

int main() {
    // 程序从 main 函数开始执行，下面的语句会按顺序运行。

	test01();


	// 返回 0 表示程序正常结束。
	return 0;
}

Operation result:

反转前：
10 30 50 20 40
反转后：
40 20 50 30 10

**Summary:** `reverse` reverses the elements within the interval; this may be covered in interview questions.

1.5.Common copy and replace algorithms

Learning Objectives:

Master commonly used copy and replace algorithms

Algorithm Introduction:

copy // Copy the elements in the specified range within the container to another container
replace // Modify the old elements in the specified range within the container to new elements
replace_if // Replace the elements that meet the condition in the specified range within the container with new elements
swap // Swap the elements of two containers

1.5.1.copy

Function description:

Copy the elements in the specified range from one container to another container.

Function prototype:

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

// Find an element by value; if found, return an iterator to the specified position; if not found, return the end iterator position

// beg Start iterator

// end End iterator

// dest Target start iterator

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

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() {
    // 程序从 main 函数开始执行，下面的语句会按顺序运行。

	test01();


	// 返回 0 表示程序正常结束。
	return 0;
}

Operation result:

1 2 3 4 5 6 7 8 9 10

**Summary:** When using the copy algorithm for copying, remember to allocate space for the target container in advance

1.5.2.replace

Function description:

Modify the old elements within the specified range in the container to new elements

Function prototype:

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

// Replace old elements in the range with new elements

// beg Start iterator

// end End iterator

// oldvalue Old element

// newvalue New element

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

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 << "替换前：" << endl;
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;

	//将容器中的20 替换成 2000
	cout << "替换后：" << endl;
	replace(v.begin(), v.end(), 20,2000);
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;
}

int main() {

	test01();


	return 0;
}

Operation result:

替换前：
20 30 20 40 50 10 20
替换后：
2000 30 2000 40 50 10 2000

**Summary:** replace replaces elements within the interval that satisfy the condition

1.5.3.replace_if

Function description:

Replace the elements in the range that satisfy the condition with the specified element.

Function prototype:

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

// Replace elements conditionally, elements that satisfy the condition are replaced with the specified element

// beg Start iterator

// end End iterator

// _pred Predicate

// newvalue New element to replace with

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

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 << "替换前：" << endl;
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;

	//将容器中大于等于的30 替换成 3000
	cout << "替换后：" << endl;
	replace_if(v.begin(), v.end(), ReplaceGreater30(), 3000);
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;
}

int main() {

	test01();


	return 0;
}

Operation result:

替换前：
20 30 20 40 50 10 20
替换后：
20 3000 20 3000 3000 10 20

**总结：**replace_if按条件查找，可以利用仿函数灵活筛选满足的条件

1.5.4.swap

Function description:

Swap the elements of two containers

Function prototype:

swap(container c1, container c2);

// Swap the elements of two containers

// c1 container 1

// c2 container 2

Example:

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

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

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

int main() {
    // 程序从 main 函数开始执行，下面的语句会按顺序运行。

	test01();


	// 返回 0 表示程序正常结束。
	return 0;
}

Operation result:

交换前：
0 1 2 3 4 5 6 7 8 9
100 101 102 103 104 105 106 107 108 109
交换后：
100 101 102 103 104 105 106 107 108 109
0 1 2 3 4 5 6 7 8 9

**Summary:** When swapping containers, ensure that the containers being swapped are of the same type.

1.6.Common arithmetic generation algorithms

Learning Objectives:

Master commonly used arithmetic generation algorithms

Note:

Arithmetic generation algorithms belong to small algorithms; the header file to include when using them is #include <numeric>

Algorithm Introduction:

accumulate // Compute the cumulative sum of container elements
fill // Add elements to the container

1.6.1.accumulate

Function description:

Calculate the cumulative sum of container elements within the range

Function prototype:

accumulate(iterator beg, iterator end, value);

// Calculate the cumulative sum of container elements

// beg Start iterator

// end End iterator

// value Initial value

Example:

#include <iostream>
#include <numeric>
#include <vector>

using namespace std;

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() {
    // 程序从 main 函数开始执行，下面的语句会按顺序运行。

	test01();


	// 返回 0 表示程序正常结束。
	return 0;
}

Operation result:

total = 5050

**Summary:** When using accumulate, note that the header file is numeric. This algorithm is very practical.

1.6.2.fill

Function description:

Fill the container with the specified elements

Function prototype:

fill(iterator beg, iterator end, value);

// Fill elements into the container

// beg Begin iterator

// end End iterator

// value Value to fill

Example:

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

using namespace std;

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

void test01()
{

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

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

int main() {

	test01();


	return 0;
}

Operation result:

100 100 100 100 100 100 100 100 100 100

**Summary:** fill can be used to fill the elements within a container range with a specified value.

1.7.Common collection algorithms

Learning Objectives:

Master commonly used collection algorithms

Algorithm Introduction:

set_intersection // Find the intersection of two containers
set_union // Find the union of two containers
set_difference // Find the difference of two containers

1.7.1.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: Both sets must be ordered sequences

// beg1 Iterator to the beginning of container 1 // end1 Iterator to the end of container 1 // beg2 Iterator to the beginning of container 2 // end2 Iterator to the end of container 2 // dest Iterator to the beginning of the destination container

Example:

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

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;
	//取两个里面较小的值给目标容器开辟空间
	vTarget.resize(min(v1.size(), v2.size()));

	//返回目标容器的最后一个元素的迭代器地址
	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();


	return 0;
}

Operation result:

5 6 7 8 9

Summary:

The two sets whose intersection is to be computed must be ordered sequences
The space to be allocated for the target container needs to be taken fromthe smaller value of the two containers
set_intersection The return value is also the position of the last element in the intersection

1.7.2.set_union

Function description:

Find the union of two sets

Function prototype:

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

// Compute the union of two sets

// Note: Both sets must be ordered sequences

// beg1 Iterator to the beginning of container 1 // end1 Iterator to the end of container 1 // beg2 Iterator to the beginning of container 2 // end2 Iterator to the end of container 2 // dest Iterator to the beginning of the destination container

Example:

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

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;
	//取两个容器的和给目标容器开辟空间
	vTarget.resize(v1.size() + v2.size());

	//返回目标容器的最后一个元素的迭代器地址
	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();


	return 0;
}

Operation result:

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Summary:

求并集的两个集合必须的有序序列
目标容器开辟空间需要两个容器相加
set_union返回值既是并集中最后一个元素的位置

1.7.3.set_difference

Function description:

Find the difference of two sets

Function prototype:

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

// Compute the difference of two sets

// Note: Both sets must be ordered sequences

// beg1 Iterator to the beginning of container 1 // end1 Iterator to the end of container 1 // beg2 Iterator to the beginning of container 2 // end2 Iterator to the end of container 2 // dest Iterator to the beginning of the destination container

Example:

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

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;
	//取两个里面较大的值给目标容器开辟空间
	vTarget.resize( max(v1.size() , v2.size()));

	//返回目标容器的最后一个元素的迭代器地址
	cout << "v1与v2的差集为： " << 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与v1的差集为： " << 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();


	return 0;
}

Operation result:

v1与v2的差集为：
0 1 2 3 4
v2与v1的差集为：
10 11 12 13 14

Summary:

求差集的两个集合必须的有序序列
目标容器开辟空间需要从两个容器取较大值
set_difference返回值既是差集中最后一个元素的位置