STL (Standard Template Library) is the standard template library of C + +. Many common data structures and algorithms in the competition are available in STL. Mastering them skillfully can greatly simplify programming in many topics.

The vector container is a template class that can hold any type of object.

I. definition

1. Define an int array (also char, double, etc.)

#include<iostream>
#include<vector>
using namespace std;
int main()
{
	vector< int >a;//Default initialization, a is empty
	vector< int >b(a);//Using a to define b
	vector< int >a(100);//A has 100 elements with a value of 0
	vector< int >a(100,6);//A has 100 elements with a value of 6
	
}

1. Defining an array of type string

#include<iostream>
#include<vector>
using namespace std;
int main()
{

	vector< string >a(10,"null");//10 elements with null values;
 	vector< string >vec(10,"hello");//10 elements with a value of hello
 	vector< string >b(a.begin(),a.end());//b is a copy of a
}

1. Defining structural arrays

#include<iostream>
#include<vector>
using namespace std;
struct point{
	int x,y;
};
int main()
{
	vector< point >a;//a is used to store coordinates
}

1. Define 2D array

	vector<int>a[5];

Simple application:

#include<bits/stdc++.h>
#include<vector>//May not write
using namespace std;
int main()
{
 	vector<int>a[10];
 	for(int i=0;i<5;i++)
 	{
  		for(int j=0;j<4;j++)
 		{
   			a[i].push_back(5);
  		}
 	} 
 	for(int i=0;i<5;i++)
	{
  		for(int j=0;j<4;j++)
  		{
   			cout<<a[i][j]<<" ";
  		}
 		cout<<endl;
 	}
}

2, Common operations

1. Assignment: add element at the end

	a.push_back(1);

1. Element number

	int size;
	size=a.size();
	cout<<size;

1. Judge whether it is empty

	bool isEmpty;
	isEmpty=a.empty();
	cout<<isEmpty;//If it is empty, return 1, otherwise return 0

1. Print first element

cout<<a[0]<<endl;

1. Insert in the middle: insert k before the i-th element

	
	a.insert(a.begin()+i,k);

1. Tail insertion

Insert single element

	 a.push_back(100);

Insert multiple elements

 	a.push_back(10，5);

1. Delete tail

	a.pop_back();

1. Delete interval: delete the element of interval [I, J-1]

	a.erase(a.begin()+i,a.begin()+j);//Elements i to j-1 are deleted

1. Delete element: delete the i+1 element

	 a.erase(a.begin()+i);

1. Resize: array size to n

	a.resize(n);

1. Sorting: from small to large (based on fast sorting)

	sort(a.begin,a.end);

1. Flipped array

	reverse(a.begin,a.end);

1. empty

	a.clear();

3, Code implementation

The following is the code implementation result and detailed code corresponding to the above:

#include<bits/stdc++.h>
#include<vector>
using namespace std;
int main()
{
   
  vector<int>a;
  a.push_back(100);
  a.push_back(101);
  a.push_back(102);

  cout<<"Number of elements:"; 
  int size=a.size();
  cout<<size<<endl;
  
  cout<<"Judge whether it is empty:";
  bool isEmpty=a.empty();
  cout<<isEmpty<<endl;
  
  cout<<"Print the first element:";
  cout<<a[0]<<endl;
  
  cout<<"Middle insertion:";
  a.insert(a.begin()+1,520);
  cout<<"Insert 520 before the first element and output four elements:"; 
  cout<<a[0]<<" "<<a[1]<<" "<<a[2]<<" "<<a[3]<<endl;
  
  cout<<"Tail insert 10 5"<<endl;
  a.insert(a.end(),10,5);
  cout<<"Insert successfully!"<<endl;
   
  cout<<"Delete interval[0,1]The first two elements are:";
  a.erase(a.begin()+0,a.begin()+2);
  cout<<a[0]<<" "<<a[1]<<endl;
  
  cout<<"The array size changes to:";
  a.resize(20);
  cout<<a.size()<<endl;
  
  cout<<"Sort the first five elements:";
  sort(a.begin(),a.begin()+5);
  cout<<a[0]<<" "<<a[1]<<" "<<a[2]<<" "<<a[3]<<" "<<a[4]<<endl;
  
  cout<<"Flip the first five elements:";
  reverse(a.begin(),a.begin()+5); 
  cout<<a[0]<<" "<<a[1]<<" "<<a[2]<<" "<<a[3]<<" "<<a[4]<<endl;
  
  cout<<"Empty the array and change the size to:";
  a.clear();
  cout<<a.size(); 
}