Skip to content
Related Articles

Related Articles

Difference between Queue and Deque in C++
  • Difficulty Level : Easy
  • Last Updated : 14 Dec, 2020

Queue: A Queue is a linear data structure that follows a First In First Out (FIFO) order in which the operations are performed. It is a type of container adaptor where elements are inserted into one end of the container and deleted from the other.

Functions:

  • empty(): Tests whether the queue is empty.
  • size(): Returns the unsigned int, size of the queue.
  • queue::front() and queue::back(): front() function returns a reference to the first element or the oldest of the queue. back() function returns a reference to the last or the newest element of the queue.
  • push(k) and pop(): push() function adds the element ‘k’ at the end of the queue. pop() function deletes the element from the beginning of the queue and reduces its size by 1.
  • swap(): exchanges the elements of two different queues of the same type but may or may not of the same size.
  • emplace(): it is used to insert a new element at end of the queue.

Syntax:

queue <data_type> q

Below is the program to illustrate the same:



C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ program to demonstrate the
// working of queue
#include <bits/stdc++.h>
using namespace std;
  
// Driver Code
int main()
{
    // Declare a queue
    queue<int> q;
  
    // Insert elements in the queue
    q.push(10);
    q.push(5);
    q.push(15);
    q.push(1);
  
    // Delete elements from the queue
    q.pop();
    q.pop();
  
    cout << "Elements in Queue are: ";
  
    // Print the element stored
    // in queue
    while (!q.empty()) {
        cout << q.front() << ' ';
  
        // Pop the front element
        q.pop();
    }
  
    return 0;
}

chevron_right


Output:

Elements in Queue are: 15 1

Deque: Deque is a sequence container with the ability of expansion and contraction on both ends. It is a template of Standard Template Library or STL in C++is. It is similar to vectors but are more efficient for the insertion and deletion of elements. Contiguous storage allocation in deque may not be guaranteed as in vectors.

Functions:

  • max_size(): Returns the maximum number of elements deque can contain.
  • push_back() and push_front(): push_front( ) push the elements into a deque from the front and push_back( ) push elements into a deque from the back.
  • pop_front() and pop_back(): pop_front() function is used to pop elements from a deque from the front and pop_back( ) function is used to pop elements from a deque from the back.
  • clear() and erase():  clear is used to remove all the elements from the deque and erase is used to remove some specified elements.
  • insert(): increases the container side by inserting element in the specified position.
  • resize(): changes the size of the element’s container as per requirement.
  • rbegin() and rend(): rbegin() points to the last element of the deque whereas rend points to the position before the beginning of the deque.
  • at() and swap(): at() points to the position of the element given in the parameter and swap( ) is used two swap elements of two deques.
  • emplace_front() and emplace_back(): these two functions are used to insert new elements in the container at the beginning and at the end of deque respectively.

Syntax:

deque<data_type> dq

Below is the program to illustrate the same:

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ program to demonstrate the
// working of deque
#include <bits/stdc++.h>
using namespace std;
  
// Driver Code
int main()
{
    // Declare a deque
    deque<int> dq;
  
    // Insert element in the front
    dq.push_front(10);
    dq.push_front(5);
    dq.push_front(3);
  
    // Delete elements from the the front
    dq.pop_front();
    dq.pop_front();
  
    // Insert elements in the back
    dq.push_back(1);
    dq.push_back(50);
    dq.push_back(2);
  
    // Delete elements from the the back
    dq.pop_back();
    dq.pop_back();
  
    cout << "Elements in deque are: ";
  
    // Print the element stored
    // in deque
    while (!dq.empty()) {
        cout << " " << dq.front();
        dq.pop_front();
    }
  
    return 0;
}

chevron_right


Output:

Elements in deque are:  10 1

Below is the tabular difference between the queue and deque:

S.No.

Queue

Deque

1 Insertion can be done through the front end only. Insertion is possible through both ends.
2 Deletion of elements is possible through the front end only. Deletion of elements possible through both ends.
3 Elements can not be accessed through iterators. Elements can be accessed through iterators.
4 Implemented as container adaptors. Implemented generally as some form of a dynamic array.
5 The stack can not be implemented using a queue. A stack can be implemented using deque.

Attention reader! Don’t stop learning now. Get hold of all the important C++ Foundation and STL concepts with the C++ Foundation and STL courses at a student-friendly price and become industry ready.

My Personal Notes arrow_drop_up
Recommended Articles
Page :