# C + + improve programming -- STL common algorithm: common sorting algorithm

Posted by admin on Mon, 07 Mar 2022 18:24:47 +0100

# 3. Common sorting algorithms

learning objective: master common sorting algorithms.

introduction to algorithm:

• Sort   / / sort the elements in the container
• random_shuffle    / / shuffle and randomly adjust the order of elements within the specified range
• 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 iterator
// _ Pred predicate

examples are as follows.

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

//Common sorting algorithm: sort

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);

//Ascending order using sort
sort(v.begin(), v.end());
for_each(v.begin(), v.end(), myPrint);
cout << endl;

//Change to descending order
sort(v.begin(), v.end(), greater<int>());
for_each(v.begin(), v.end(), myPrint);
cout << endl;
}

int main()
{
test01();

system("pause");

return 0;
}
```

10 20 30 40 50
50 40 30 20 10

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

## 3.2 random_shuffle

Function Description: shuffle and randomly adjust the order of elements within the specified range.

function prototype: random_shuffle(iterator beg, iterator end);
/ / randomly adjust the order of elements within the specified range
/ / beg start iterator
/ / end iterator

examples are as follows.

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

//Common sorting algorithm: random_shuffle

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

void test01()
{
srand((unsigned)time(NULL));

vector<int>v;

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

//Using random_shuffle shuffle algorithm disrupts the order
random_shuffle(v.begin(), v.end());
for_each(v.begin(), v.end(), myPrint);
cout << endl;
}

int main()
{
test01();

system("pause");

return 0;
}
```

7 8 6 5 3 2 4 0 9 1

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

## 3.3 merge

Function Description: two container elements are merged and stored 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 be in order
/ / beg1 container 1 starts iterator
/ / end1 container 1 end iterator
/ / beg2 container 2 starts iterator
/ / end2 container 2 end iterator
/ / dest target container starts iterator

examples are as follows.

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

//Common sorting algorithm: merge

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 + 1);
}

//Target container
vector<int>vTarget;

vTarget.resize(v1.size() + v2.size());  //The target container needs to open up space in advance

//merge two containers v1 and v2 and store them in another container vTarget
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;
}
```

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

summary: 1 The two containers merged by merge must be an ordered sequence;
2. The target container needs to open up space in advance.

## 5.3.4 reverse

Function Description: invert the elements in the container.

function prototype: reverse(iterator beg, iterator end);
/ / reverses the elements of the specified range
/ / beg start iterator
/ / end iterator

examples are as follows.

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

//Common sorting algorithm: reverse

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);

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

//Use reverse to reverse the elements in the container
reverse(v.begin(), v.end());

cout << "After reversal:" << endl;
for_each(v.begin(), v.end(), myPrint);
cout << endl;
}

int main()
{
test01();

system("pause");

return 0;
}
```

Before reversing:
10 30 50 20 40
After reversal:
40 20 50 30 10

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

Topics: C++ Programming Algorithm