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.