# 1, Common copy and replace 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 elements that meet the conditions in the specified range in the container with new elements
Swap / / swap the elements of the two containers

## 1.1 copy

Function Description: copy the elements in the specified range in the 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 cannot be found
beg: start iterator
End: end iterator
dest: target start iterator

Case: test the function of copy

```#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;

class myPrints
{
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(), myPrints());
cout << endl;
}

int main() {
test01();
system("pause");

return 0;
}
```

Run, the effect is as follows.

## 1.2 replace

Function Description: modify 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

Case: test the function of copy

```#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;

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

void test01()
{
vector<int> v;
v.push_back(10);
v.push_back(20);
v.push_back(50);
v.push_back(20);
v.push_back(40);
v.push_back(70);

for_each(v.begin(), v.end(), myPrint());
cout << endl;
replace(v.begin(), v.end(), 20, 2000);
for_each(v.begin(), v.end(), myPrint());
}

int main() {
test01();
system("pause");

return 0;
}
```

Run, the effect is as follows.

## 1.3 replace_if

Function Description: replace the elements that meet the conditions in the interval with the specified elements
Function prototype: replace_if(iterator beg, iterator end, _pred, newvalue);
Replace the elements according to the conditions, and replace the elements that meet the conditions with the specified elements
beg: start iterator
End: end iterator
_ pred: predicate
newvalue: replaced new element

Case: Test replace_ Functions of if

```#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;

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

class Greater30
{
public:
bool operator()(int val)
{
return val >= 30;
}
};

void test01()
{
vector<int> v;
v.push_back(10);
v.push_back(20);
v.push_back(50);
v.push_back(20);
v.push_back(40);
v.push_back(70);

//Replace those greater than or equal to 30 with 3000
for_each(v.begin(), v.end(), myPrint());
cout << endl;
replace_if(v.begin(), v.end(), Greater30(), 3000);
for_each(v.begin(), v.end(), myPrint());
}

int main() {
test01();
system("pause");

return 0;
}
```

Run, the effect is as follows.

## 1.4 swap

Function Description: exchange elements of two containers
Function prototype: swap(container c1, container c2);
Swap elements of two containers
c1: container 1
c2: container 2

Case: test the function of swap

```#include <algorithm>
#include <vector>
#include <iostream>
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 << "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;
}
```

Run, the effect is as follows.

# 2, Common arithmetic generation algorithm

Learning objectives: master common arithmetic generation algorithms
Note: the arithmetic generation algorithm is a small algorithm, and the header file included when using is \include <numeric>
Algorithm Introduction:
accumulate / / calculate the cumulative sum of container elements
fill / / add elements to the container

## 2.1 accumulate

Function Description: calculate the cumulative sum of interval content elements
Function prototype: accumulate(iterator beg, iterator end, value);
Calculate the cumulative sum of container elements
beg: start iterator
End: end iterator
Value: starting value (starting cumulative value, adding all subsequent values here)

Case: test the function of accumulate

```#include <numeric>
#include <vector>
#include <iostream>
using namespace std;

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

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

int a = accumulate(v.begin(), v.end(), 0);
int b = accumulate(v.begin(), v.end(), 1000);

cout << "a = " << a << "， b = " << b << endl;
}

int main() {
test01();
system("pause");

return 0;
}
```

Run, the effect is as follows.

## 2.2 fill

Function Description: fill the container with the specified elements
Function prototype: fill(iterator beg, iterator end, value);
Fill the container with elements
beg: start iterator
End: end iterator
Value: filled value

Case: test the function of fill

```#include <numeric>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

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;
}
```

Run, the effect is as follows.

# 3, Common set algorithm

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

## 3.1 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 that the two sets must be ordered sequences
beg1: container 1 start iterator
end1: container 1 end iterator
beg2: container 2 start iterator
end2: container 2 end iterator
dest: target container start iterator

Case: Test Set_ Function of intersection

```#include <numeric>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

void myPrint(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);
}
for_each(v1.begin(), v1.end(), myPrint);
cout << endl;
for_each(v2.begin(), v2.end(), myPrint);
cout << endl;

vector<int> v3;
//The container size is the smallest of the two containers
v3.resize(min(v1.size(), v2.size()));
vector<int>::iterator End = set_intersection(v1.begin(), v1.end(), v2.begin(), v2.end(), v3.begin());
for_each(v3.begin(), End, myPrint);
cout << endl;
}

int main() {
test01();
system("pause");

return 0;
}
```

Run, the effect is as follows.

## 3.2 set_intersection

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: target container start iterator

Case: Test Set_ Functions of union.

```#include <numeric>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

void myPrint(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);
}
for_each(v1.begin(), v1.end(), myPrint);
cout << endl;
for_each(v2.begin(), v2.end(), myPrint);
cout << endl;

vector<int> v3;
//The new container size is the sum of the previous two container sizes
v3.resize(v1.size() + v2.size());
vector<int>::iterator End = set_union(v1.begin(), v1.end(), v2.begin(), v2.end(), v3.begin());
for_each(v3.begin(), End, myPrint);
cout << endl;
}

int main() {
test01();
system("pause");

return 0;
}
```

Run, the effect is as follows.

## 3.3 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: target container start iterator

The definition of difference set is as follows:

Case: Test Set_ Function of difference

```#include <numeric>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

void myPrint(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);
}
for_each(v1.begin(), v1.end(), myPrint);
cout << endl;
for_each(v2.begin(), v2.end(), myPrint);
cout << endl;

vector<int> v3;
v3.resize(max(v1.size(),v2.size()));
//Difference set of v1 and v2
vector<int>::iterator End = set_difference(v1.begin(), v1.end(), v2.begin(), v2.end(), v3.begin());
for_each(v3.begin(), End, myPrint);
cout << endl;
//Difference set of v2 and v1
End = set_difference(v2.begin(), v2.end(), v1.begin(), v1.end(), v3.begin());
for_each(v3.begin(), End, myPrint);
cout << endl;
}

int main() {
test01();
system("pause");

return 0;
}
```

Run, the effect is as follows.

Posted by mbarmawi on Mon, 08 Aug 2022 02:51:25 +0930