Explain double ended queue in detail

Introduction:

Commonly called deques (pronounced "deck"), double-ended queues are adaptable data structures that are essential to computer science and programming. Data collections can be effectively managed and manipulated with the help of deques, which offer dynamic storage capabilities that let elements be added or removed from both ends. We shall examine the construction, functions, and real-world uses of a double-ended queue in detail in this article.

The Deque's Structure:

A linear data structure called a deque combines the advantages of queues and stacks. Usually, it is implemented as a linked list or an array. A deque's capacity to do insertion and removal operations at both ends distinguishes it as a unique instrument with numerous applications. Deques enable constant-time operations for both front and back insertions and removals, unlike arrays or linked lists.

Key Operations:

Deques allow for the addition of elements both at the front and the back of the data structure. In situations where items must be added dynamically on both ends, this process is crucial.
Similarly, deques offer the flexibility to remove pieces from both the front and the rear, enabling effective data management.
A deque's elements can be accessed from either the front or the back, as well as from any arbitrary location within the deque.
Deques provides techniques for measuring structure sizes, which are crucial for controlling and optimizing memory utilization.

Practical Applications:

Task Scheduling: Operating systems and task scheduling algorithms frequently use deques. A balanced approach to task management can be achieved by moving older activities from the back of the deque and adding new tasks to the front.
Browser Navigation History: To preserve the user's navigation history, browsers use deques. The deque effectively manages forwarding and reversing through web pages, enabling rapid navigation.
Data Structures: Deques are a fundamental building component for more complex data structures like double-ended priority queues, which come in handy when elements must be sorted in a certain order.
Implementing Queues and Stacks: Queues and stacks can be implemented using Deques. You may simulate the behavior of a queue (FIFO) or stack (LIFO) by utilizing only the front or back operations.
Algorithm Optimization: Deques plays a key part in algorithm optimization. For instance, deques are effectively employed in sliding window algorithms to retain the maximum or minimum components within a sliding window of data.
Undo and Redo Functionality: The undo and redo features are often implemented using deques in software applications like text editors and graphic design programs. A deque is used to store changes to the application state, letting users go back and forth between their actions.
Games and simulations: Deque can be used to manage events, actions, and state changes in games and simulations. They enable effective state management and event handling.

Implementation Details:

Data structures like dynamic arrays, linked lists, and arrays can all be used to build deques. The particular requirements of the application will determine the implementation to be used.

Implementation Using an Array: A deque can be implemented using a static or dynamic array. If the array fills capacity in a fixed-size array, resizing may become problematic. Resizing and memory management are taken care of automatically via dynamic arrays like Python's collections.deque.

Implementation of a Linked List: In an implementation of a Linked List, each element is represented by a node that includes the element and links to the elements before and after it. As no pieces need to be moved, this enables effective insertion and removal at either end.

Complexity Assessment:

Deque operations' time complexity varies depending on the implementation and can be as follows:

Insertion and removal: When the array needs to be resized, these operations may, in the worst case, cost O(n) in the array-based implementation. They are usually O(1) in a linked list-based implementation.
Accessing Elements: Because you may directly access elements by their index, accessing elements in both array-based and linked list-based deques is O(1).

Advantages of Deques:

Efficiency: Deques are extremely effective data structures for adding and deleting components from both ends. They are preferred under conditions when performance is crucial since they offer O(1) time complexity for certain operations.
Versatility: Deques combine the advantages of both queues and stacks, making them extremely versatile. As general-purpose data structures, they provide adaptable data management.
No Wasted Memory: Deques optimize memory consumption by dynamically expanding the underlying storage, in contrast to dynamic arrays which may allocate more memory than necessary.

Different forms of Deques:

Circular Deque: Deque implementation using a circular array structure is known as a circular deque. It is especially memory-efficient because it enables efficient element addition and removal without necessitating array resizing. The circular strategy makes managing the pieces at both ends easier.
Priority Queue with Deque:A deque-based priority queue enables you to handle a group of elements with different priorities. In situations when it is necessary to handle items according to their priority levels, this data structure is quite helpful.
Deque with Limited Capacity: You might want to establish a deque with a limited capacity in some situations. This is helpful if you need to keep a sliding window of data open or make sure the deque doesn't get too big.

Challenges and Considerations:

Memory Overhead: When resizing is frequent, dynamic arrays and linked list-based queues may have memory overhead. The trade-off between memory utilization and performance should be taken into account by developers.
Concurrency: To avoid data corruption or race circumstances while employing deques in multi-threaded programs, thread-safe operations must be implemented.
Selecting the Appropriate Implementation: The implementation (array-based or linked list-based) should be selected depending on the application's particular requirements. For instance, linked list-based deques are better at handling frequent insertions and removals while array-based deques are typically faster for random access.

C Implementation of Deque:

#include <stdio.h>
#include <stdlib.h>
#define MAX_SIZE 100
struct Deque {
    int arr[MAX_SIZE];
    int front, rear;
};
void initialize(struct Deque *dq) {
    dq->front = -1;
    dq->rear = -1;
}
int is_empty(struct Deque *dq) {
    return (dq->front == -1);
}
int is_full(struct Deque *dq) {
    return ((dq->front == 0 && dq->rear == MAX_SIZE - 1) || (dq->front == dq->rear + 1));
}
void insert_front(struct Deque *dq, int item) {
    if (is_full(dq)) {
        printf("Deque is full, insertion failed.\n");
        return;
    }
    if (dq->front == -1) {
        dq->front = 0;
        dq->rear = 0;
    } else if (dq->front == 0) {
        dq->front = MAX_SIZE - 1;
    } else {
        dq->front--;
    }
    dq->arr[dq->front] = item;
}
void insert_rear(struct Deque *dq, int item) {
    if (is_full(dq)) {
        printf("Deque is full, insertion failed.\n");
        return;
    }
    if (dq->front == -1) {
        dq->front = 0;
        dq->rear = 0;
    } else if (dq->rear == MAX_SIZE - 1) {
        dq->rear = 0;
    } else {
        dq->rear++;
    }
    dq->arr[dq->rear] = item;
}
int delete_front(struct Deque *dq) {
    if (is_empty(dq)) {
        printf("Deque is empty, deletion failed.\n");
        return -1;
    }
    int item = dq->arr[dq->front];
    if (dq->front == dq->rear) {
        dq->front = -1;
        dq->rear = -1;
    } else if (dq->front == MAX_SIZE - 1) {
        dq->front = 0;
    } else {
        dq->front++;
    }
    return item;
}
int delete_rear(struct Deque *dq) {
    if (is_empty(dq)) {
        printf("Deque is empty, deletion failed.\n");
        return -1;
    }
    int item = dq->arr[dq->rear];
    if (dq->front == dq->rear) {
        dq->front = -1;
        dq->rear = -1;
    } else if (dq->rear == 0) {
        dq->rear = MAX_SIZE - 1;
    } else {
        dq->rear--;
    }
    return item;
}
int size(struct Deque *dq) {
    if (dq->front == -1) {
        return 0;
    } else if (dq->front <= dq->rear) {
        return dq->rear - dq->front + 1;
    } else {
        return (MAX_SIZE - dq->front) + (dq->rear + 1);
    }
}
int main() {
    struct Deque dq;
    initialize(&dq);
    insert_rear(&dq, 1);
    insert_front(&dq, 2);
    insert_rear(&dq, 3);
    printf("Deque size: %d\n", size(&dq));
    printf("Front element: %d\n", delete_front(&dq));
    printf("Rear element: %d\n", delete_rear(&dq));
    printf("Deque size: %d\n", size(&dq));
    return 0;
}

Output:

Deque size: 3
Front element: 2
Rear element: 3
Deque size: 1

Conclusion:

Deques, or double-ended queues, are fundamental data structures with a wide range of management and manipulation options. They are a useful tool for programmers and computer scientists due to their effectiveness in handling aspects at both ends. Deques are used in many areas of computer science and programming because they effectively add and remove items from both ends. Any programmer or computer scientist looking to maximize data management and access must be familiar with their structure, fundamental operations, real-world applications, and implementation specifics. Deques are a useful tool in a programmer's toolbox since they allow for efficient and flexible data handling.

Next TopicFind the median from running data stream

← prev next →