Deque in STL C++

July 25, 2023

About Deque in STL :

Deque in STL is defined as the container used to insert and remove elements at both ends. They are implementing using queue data structure.

Introduction to Deque in C++

Deque, short for “Double-Ended Queue,” is an essential data structure in C++ provided by the Standard Template Library (STL). It shares similarities with vectors and lists but offers additional benefits due to its versatile nature. A Deque allows elements to be inserted or removed from both ends efficiently, making it an excellent choice for various applications.

Advantages of using Deque:

Dynamic Size: Unlike arrays, Deque can change its size dynamically, making it more flexible in handling varying amounts of data.

Fast Insertions and Deletions: Deque enables fast insertions and deletions at both ends, providing efficient data manipulation.

Random Access: Like vectors, Deque allows for direct access to elements using indexing, ensuring quick element retrieval.

Memory Efficiency: Deque optimizes memory utilization, making it an ideal choice for large-scale applications.

Functions in Deque :

Function	Working
push_back()	insert an element to the back end of the deque.
push_front()	insert an element to the front end of the deque.
size()	give the number of elements present in the deque.
empty()	tells whether the deque is empty or not.
max_size()	return the maximum number of elements can deque hold.

Basic Operations on Deque

Initializing a Deque:

To use a Deque, we need to include the header file in our C++ program. We can then create a Deque object using its constructor.

Run

#include < iostream >
#include < deque >

int main() {
    std::deque<int> myDeque; // Initializing an empty integer Deque
    return 0;
}

Insertion and Deletion of Elements:

Deque supports several methods for inserting and removing elements. Some commonly used functions include push_back(), push_front(), pop_back(), and pop_front(). Insertion and Deletion of Elements:

Run

#include <iostream>
#include <deque>
int main() {
    std::dequemyDeque;

    myDeque.push_back(10);    // Insert 10 at the end
    myDeque.push_front(5);    // Insert 5 at the beginning

    myDeque.pop_back();       // Remove the last element
    myDeque.pop_front();      // Remove the first element

    return 0;
}

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Accessing Elements in Deque:

Elements in a Deque can be accessed using the subscript operator [] or the at() function.

Run

#include <iostream>
#include <deque>

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

    myDeque.push_back(10);
    myDeque.push_back(20);
    myDeque.push_back(30);

    int elementAtIndex1 = myDeque[1]; // Access the element at index 1 (20)
    int elementAtIndex2 = myDeque.at(2); // Access the element at index 2 (30)

    return 0;
}

Implementation of Deque in STL

The C++ Standard Template Library (STL) provides a rich set of classes and functions to work with data structures like Deque.

Code example of Deque implementation:

Run

#include <iostream>
#include <deque>

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

    myDeque.push_back(10);
    myDeque.push_back(20);
    myDeque.push_front(5);

    std::cout << "Front element: " << myDeque.front() << std::endl; // Output: Front element: 5
    std::cout << "Back element: " << myDeque.back() << std::endl;   // Output: Back element: 20

    return 0;
}

Use Cases of Deque in C++

Deque finds applications in various scenarios due to its unique characteristics. Real-world scenarios for Deque:

Task Scheduling: Deque can be used in task scheduling algorithms, where new tasks can be added or removed efficiently from both ends.

Sliding Window Technique: Deque is commonly used to solve problems involving sliding window algorithms, where elements move in a fixed-size window.

Undo/Redo Operations: Deque’s ability to insert and remove elements from both ends makes it suitable for implementing undo and redo functionalities in applications.

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