Some practical operations of vector

#include <vector>
using namespace std;

establish 、 Copy

vector<int> a;        // Create an empty vector
vector<int> a(n);     // Create a containing n Object's vector,
                      // At this time, the data has been generated by default , For example, the current array is full of 0
vector<int> a(n, elem);// Create a containing n individual elem Copy vector

vector<int> a1(a2);   // Copy a vector
vector<int> a1(begin, end); // take [begin,end) Copy the data in the range 

visit

a.begin()         Returns a pointer to the first object , That is commonly known as iterators 
a.end()           Returns a pointer to the next position of the last object 
a.begin()+1       Returns a pointer to the next object of the first object 
a.end()-1         Returns a pointer to the last object 

a.rbegin()        Returns a pointer to the last object , reverse iterator 
a.rend()          Returns a pointer to the previous position of the first object , reverse iterator 

a.front()         Return the data of the first object , and *a.begin() It's the same 
a.back()          Return the data of the last object 
a.at(i)           Return number i Object data at location , Will check whether the data exists 
a[i]              Return number i Object data at location 

Insert

a.push_back(i);            // The simplest insertion , Direct to vector Add a data at the end 
a.insert(pos,elem);        // towards pos Insert an object before the object pointed to by the iterator , Attention is in front of the object 
a.insert(pos, n, elem);    // towards pos Insert before the object pointed to by the iterator n Same objects 
a.insert(pos, begin, end); // towards pos Insert before the object pointed to by the iterator [begin,end) Between the objects 
 The last three functions will return the location of the new data 

Delete

a.clear();                 // Delete all objects 
a.pop_back();              // Delete the last object 
a.erase(pos);              // Delete pos The object corresponding to the iterator 
a.erase(begin, end);       // Delete [begin,end) Between the objects 
 The last two functions will return the next location of the deleted data 

Be careful , Both insert and delete will result in an iterator pointing to the position after the inserted or deleted iterator , The pointer , Citation failure such as

start = a.begin(); end = a.end(); a.insert(start, elem);
// stay begin Insert data before a.erase(start, end); // Will report a mistake , Because at this time end It's invalid
After the above code is reordered, it can be run ：

start = a.begin(); end = a.end(); it = a.erase(start, end);
// Save the deleted iterator a.insert(it, elem); // stay it Insert data before It's here for convenience , There is no specific type of write iterator

assignment

a[1] = 1;            // Order No 1 The object data of is 1
a.assign(1, 1);      // Make a by {1}
a.assign(begin,end); // Put the other vector in [begin,end) The data in is assigned to a
 Note that the results of the first and second lines are completely different ,assign Function is a bit similar to copy function , It is the operation of the whole 

Other common functions :size、empty、swap、sort

a.size()         return vector The number of elements in 
a.empty()        return vector Is it empty , Empty return 1, Not empty return 0
a1.swap(a2);     // In exchange for a1,a2 data 
swap(a1, a2);    // In exchange for a1,a2 data , ditto 
swap(a1[1], a1[2]);    // In exchange for a1 Of the 2 Data and 3 Data  
sort(begin, end);      // Yes [begin,end) Sort the data in the range