Double-Ended Queue

Definition of Double-Ended Queue

A double-ended queue, also known as a deque (pronounced “deck”), is a data structure that allows the addition and removal of elements from both its ends, offering greater flexibility than a traditional queue or stack. It combines the functionality of both these structures, enabling efficient insertion and deletion at the front and rear. Deques are often used in applications that require constant-time access to both ends of the collection, such as in certain algorithms or data manipulation tasks.


The phonetic pronunciation of the keyword “Double-Ended Queue” is:/ˈdʌbəl ˈɛndɪd kjuː/

Key Takeaways

  1. A double-ended queue (deque) is a data structure that allows items to be added or removed from both its ends, providing a flexible and efficient way to manipulate elements.
  2. Deques can be used to implement various data structure operations like stacks, queues, and even lists, while supporting fast constant-time access, insertion, and removals at both ends.
  3. Use cases for deques include efficient processing of series data, cache mechanisms, and specific problems that require palindrome or sliding window algorithms.

Importance of Double-Ended Queue

The term Double-Ended Queue (often abbreviated as Deque) is important in technology because it refers to a highly versatile linear data structure that allows elements to be easily added or removed from both its ends.

Deques provide a unique combination of stack and queue operations, making them ideal for scenarios requiring flexibility and efficiency in numerous algorithms and applications, such as managing resources in multitasking environments, implementing caches, and supporting advanced data manipulation functions in programming libraries.

By enabling dynamic adaptability, Deques contribute significantly to optimizing system performance and streamlining software development processes.


Double-Ended Queue, also known as Deque (pronounced as “deck”), is a versatile data structure that serves a specific purpose in the realm of computer programming and software development. With a unique attribute of being able to perform operations on both its ends, it offers an efficient and flexible way to manage and manipulate elements within the data structure.

The primary purpose of a Deque is to provide programmers with greater control over the insertion and deletion of elements, enabling seamless execution of specific algorithms, catering to various programming scenarios, and ensuring optimization in terms of speed and resource utilization. In practice, Deque is widely employed across diverse applications, ranging from simple implementation as a general-purpose data structure to more complex scenarios such as scheduling tasks or solving sliding window problems.

It is particularly useful for situations that require quick access to both the first and the last elements of a sequence or when elements need to be added or removed dynamically at either end. Additionally, the Deque implementation can be customized to be either doubly-linked or circular, further enhancing its flexibility to adapt to the unique requirements of varied programming challenges.

In summary, Double-Ended Queue stands out as an invaluable tool in the developer’s arsenal, enabling efficient and adaptable solutions to real-world programming problems.

Examples of Double-Ended Queue

A double-ended queue (deque) is a flexible data structure that allows elements to be added or removed from both ends efficiently. Here are three real-world examples of its implementation:

Web Browsing History: Modern web browsers often use deques to manage a user’s browsing history. When a user navigates to a new webpage, the browser adds the new URL to the front of the browse history deque, while also allowing the user to go back to previously visited pages by removing the last element from the back of the deque. This makes navigation quick and simple, as users can easily go back and forth through their browsing history.

Task Scheduling in Operating Systems: Some operating systems utilize deques for task scheduling, when managing multiple tasks with different priorities. For example, high-priority tasks can be added to the front of the deque, while low-priority tasks are added to the back. The processor then executes tasks from the front of deque, ensuring high-priority tasks are always executed first. Deques can also maintain flexibility by allowing the addition or removal of tasks with different priorities at either end without reorganizing the entire structure.

Undo/Redo Functionality in Software Applications: Many software applications, including text editors and graphic design tools, use deques to implement the undo/redo functionality. Whenever a user performs an action, the application records the action and stores it in a deque. If the user later wishes to undo an action, the software can retrieve the action from the back of the deque and reverse it. Similarly, redoing involves retrieving actions from the front of the undo deque and applying them again. This allows for efficient management of undo/redo operations, minimizing the need to traverse an entire list of actions every time.

Double-Ended Queue FAQ

1. What is a double-ended queue?

A double-ended queue (deque) is a data structure that allows you to insert and remove elements from both the front and the rear of the queue. It allows for efficient manipulation of data because you can easily add or remove elements at either end without moving the entire list, like you would have to in a single-ended queue.

2. When would you use a double-ended queue?

Double-ended queues can be used in a variety of situations including algorithms, implementing data buffers, managing processes in operating systems, and scheduling tasks. They are particularly useful in cases where you need to maintain a list of elements with the flexibility to add or remove items from both ends of the list depending on the specific problem requirements.

3. How can you implement a double-ended queue?

A double-ended queue can be implemented using an array or a doubly-linked list. An array-based implementation will have faster access times, but can suffer from capacity limitations and resizing issues. A doubly-linked list implementation will allow for easier adjustment of the deque size and avoid resizing issues but with slightly slower access times when compared to an array implementation.

4. What is the time complexity of operations in a double-ended queue?

The time complexity of operations in a double-ended queue depends on the implementation. In an array-based implementation, the time complexity is O(1) for adding or removing elements at both ends, but it can be O(n) for reallocations when the array capacity is reached. In a doubly-linked list implementation, adding or removing elements at both ends generally takes O(1) time, since no resizing is required.

5. What are the advantages and disadvantages of using a double-ended queue?

Advantages include:

  • Flexibility to manipulate data at both ends of the list
  • Reduced need for data movement compared to single-ended queues
  • Efficient in various algorithms and data management tasks

Disadvantages include:

  • Higher implementation complexity compared to a single-ended queue
  • Potential resizing issues with array-based implementations
  • Slower access times for certain operations with doubly-linked list implementation

Related Technology Terms

  • Deque Operations
  • Front and Rear Ends
  • Deque Implementations
  • Dynamic Memory Allocation
  • Circular Buffer

Sources for More Information

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