Queue vs. deque (double-ended queue) in C++

10 Oct 2023

datastructures

In C++, there are two commonly used data structures for managing collections of elements: Queue and Deque (Double-Ended Queue). While both structures have similarities, they differ in terms of how elements are inserted and removed. Understanding the differences between the two can help you choose the appropriate data structure for your specific needs.

Queue

A Queue is a data structure where elements are inserted from one end (rear) and removed from the other end (front) with the concept of “first in, first out” (FIFO). This means that the element that is inserted first will be the first one to be removed.

In C++, you can use the std::queue container from the Standard Template Library (STL) to implement a Queue. Here’s an example of how to use it:

#include <queue>

int main() {
    std::queue<int> myQueue;

    myQueue.push(10);  // Insert 10
    myQueue.push(20);  // Insert 20
    myQueue.push(30);  // Insert 30

    std::cout << myQueue.front();  // Output: 10

    myQueue.pop();  // Remove the front element

    std::cout << myQueue.front();  // Output: 20

    return 0;
}

Deque (Double-Ended Queue)

A Deque is a data structure that allows elements to be inserted or removed from both ends. It provides more flexibility compared to a Queue. You can insert or remove elements from either end (front or rear) as per your requirement.

In C++, the std::deque container from the STL can be used to implement a Deque. Here’s an example:

#include <deque>

int main() {
    std::deque<int> myDeque;

    myDeque.push_back(10);  // Insert 10 at the rear
    myDeque.push_front(20);  // Insert 20 at the front

    std::cout << myDeque.back();  // Output: 10 (rear element)
    std::cout << myDeque.front();  // Output: 20 (front element)

    myDeque.pop_back();  // Remove the rear element

    std::cout << myDeque.back();  // Output: 20

    return 0;
}

Choosing between Queue and Deque

When deciding whether to use a Queue or a Deque, consider the following:

If you need a simple FIFO structure where elements are inserted from the rear and removed from the front, a Queue is sufficient.
If you require more flexibility and need to insert or remove elements from both ends, a Deque is the better choice.

In some cases, the choice between Queue and Deque depends on the specific problem or task you are working on. Understanding the differences and capabilities of both structures will help you make an informed decision.

For more on C++ data structures and algorithms, follow #cpp #datastructures.