What is Deque?

Double Ended Queue which is also called Deque is a type of queue data structure in which the insertion and deletion of elements can be either in front or rear. 

Deque in STL.

Syntax:

deque<object_type> variable_name; 

Example:

deque<int> dq;
deque<string> dq;

Functions in Deque:

• push_back() – to insert an element at the end of the deque.

deque<int> dq;
dq.push_back(110);
dq.push_back(220);

• push_front() – to insert an element at the front of the deque.

deque<int> dq;
dq.push_front(110);
dq.push_front(220);

• pop_back() – deletes the last element of the deque.

dq.pop_back();

• pop_front() – deletes the front element of the deque.

dq.pop_front();

• front() – it gives a reference to the first element of the deque.

dq.front();

• back() – it gives a reference to the last element of the deque.

dq.back();

• size() – returns the number of elements on the deque.

dq.size();

• empty() – to check if the deque is empty or not.

dq.empty();

Code:

#include<bits/stdc++.h>
using namespace std;
void printdeque(deque<int> dq)
{
    deque<int>::iterator it;
    for(it=dq.begin();it!=dq.end();it++)
    {
        cout<<*it<<" ";
    }
    cout<<endl;
}
int main()
{
    deque<int> dq;
    dq.push_back(10);
    dq.push_back(20);
    dq.push_front(30);
    dq.push_front(40);
    dq.push_front(50);
    
    cout<<"The elements in the deque are: ";
    printdeque(dq);
    
    cout<<"The size of the deque is: "<<dq.size()<<endl;
    cout<<"The first element in the deque: "<<dq.front()<<endl;
    cout<<"Deleting the first element"<<endl;
    dq.pop_front();
    printdeque(dq);
    cout<<"The last element of the deque: "<<dq.back()<<endl;
    cout<<"Deleting the last element"<<endl;
    dq.pop_back();
    printdeque(dq);
    
}

Other functions in Deque:

• begin() – it refers to the first element of the deque.
• end() – it refers to the theoretical element after the last element of the deque.
• cbegin() – it refers to the first element of the deque.
• cend() – it refers to the theoretical element after the last element of the deque
• rbegin() – it points to the last element of the deque.
• rend() – it points to the theoretical element before the first element of the deque.
• emplace_front() – to insert an element at the front of the deque.
• emplace_back() – to insert an element at the end of the deque.
• max_size() – the maximum elements a deque can hold.
• clear() – to delete all the elements of the deque.
• erase() – to delete a single element or elements between a particular range.

Special thanks to Subhrajit Das for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article