vector rbegin() and rend() function in C++ STL

1. vector::rbegin() is a built-in function in C++ STL which returns a reverse iterator pointing to the last element in the container. 
   Syntax:
   

vector_name.rbegin()

1. Parameters: The function does not accept any parameter.
   Return value: The function returns a reverse iterator pointing to the last element in the container.
   Program to demonstrate the vector::rbegin() method: 
   Program 1: 
   

CPP

// CPP program to illustrate
// the vector::rbegin() function
#include <bits/stdc++.h>
using namespace std;

int main()
{
    vector<int> v;
    v.push_back(11);
    v.push_back(12);
    v.push_back(13);
    v.push_back(14);
    v.push_back(15);

    // prints all the elements
    cout << "The vector elements in reverse order are:\n";
    for (auto it = v.rbegin(); it != v.rend(); it++)
        cout << *it << " ";
    return 0;
}

Output:

The vector elements in reverse order are:
15 14 13 12 11

Time Complexity – constant O(1)

1. vector::rend() is a built-in function in C++ STL which returns a reverse iterator pointing to the theoretical element right before the first element in the vector container.
   Syntax:
   

vector_name.rend()

1. Parameters: The function does not take any parameter.
   Return value: The function returns a reverse iterator pointing to the theoretical element right before the first element in the vector container.
   Program to demonstrate the vector::rend() method: 
   Program 1: 
   

CPP

// CPP program to illustrate
// the vector::rend() function
#include <bits/stdc++.h>
using namespace std;

int main()
{
    vector<int> v;
    v.push_back(11);
    v.push_back(12);
    v.push_back(13);
    v.push_back(14);
    v.push_back(15);

    cout << "The last element is: " << *v.rbegin();

    // prints all the elements
    cout << "\nThe vector elements in reverse order are:\n";
    for (auto it = v.rbegin(); it != v.rend(); it++)
        cout << *it << " ";
    return 0;
}

Output:

The last element is: 15
The vector elements in reverse order are:
15 14 13 12 11

Time Complexity – constant O(1)