What Is a Dequeue in Data Structure?

A dequeue, also known as a double-ended queue, is a data structure that allows you to insert and remove elements from both ends. It combines the functionality of a stack and a queue, making it versatile and efficient for certain applications. In this article, we will explore the concept of a dequeue in depth.

What Is a Dequeue?

A dequeue is an abstract data type that can be implemented using various data structures such as arrays or linked lists. It allows insertion and deletion of elements from both the front and the rear end. This flexibility enables efficient implementation of algorithms where insertion or deletion operations need to be performed at both ends.

Operations Supported by Dequeues

A dequeue supports several operations for manipulating its contents. Some of the common operations include:

• InsertFront: Inserts an element at the front of the dequeue.
• InsertRear: Inserts an element at the rear of the dequeue.
• DeleteFront: Deletes an element from the front of the dequeue.
• DeleteRear: Deletes an element from the rear of the dequeue.
• GetFront: Retrieves the element at the front of the dequeue without removing it.
• GetRear: Retrieves the element at the rear of the dequeue without removing it.

Applications of Dequeues

Dequeues find applications in various scenarios where elements need to be inserted or removed from both ends efficiently. Some common use cases include:

• Scheduling Algorithms:
  A priority-based scheduling algorithm may require inserting processes with different priorities at either end of the dequeue.
• Sliding Window:
  When solving problems related to sliding windows, a dequeue can be used to efficiently maintain elements within the window by inserting at one end and removing from the other.
• Palindrome Checking:
  A dequeue can be used to check whether a given sequence is a palindrome by comparing elements from both ends.

Implementing a Dequeue

There are several ways to implement a dequeue. One common approach is using a doubly-linked list, where each node contains pointers to the previous and next nodes. This allows for efficient insertion and deletion operations at both ends.

Here is an example implementation of a dequeue using JavaScript:

<script>
class Dequeue {
  constructor() {
    this.items = [];
  }

  insertFront(element) {
    this.items.unshift(element);
  }

  insertRear(element) {
    this.push(element);
  }

  deleteFront() {
    if (this.isEmpty()) {
      return "Underflow";
    }
    return this.shift();
  }

  deleteRear() {
    if (this.pop();
  }

  getFront() {
    if (this.isEmpty()) {
      return "No elements in Dequeue";
    }
    return this.items[0];
  }

  getRear() {
    if (this.items[this.length - 1];
  }

  isEmpty() {
    return this.length === 0;
  }
}

const dequeue = new Dequeue();
dequeue.insertFront(10);
dequeue.insertRear(20);
dequeue.deleteFront();
dequeue.deleteRear();
</script>

In this implementation, the insertFront method inserts an element at the front of the dequeue, insertRear inserts an element at the rear, deleteFront deletes an element from the front, and deleteRear deletes an element from the rear. The getFront and getRear methods retrieve elements from the front and rear respectively without removing them. Finally, the isEmpty method checks if the dequeue is empty.

In Conclusion

A dequeue is a versatile data structure that supports efficient insertion and deletion operations at both ends. It combines the functionality of a stack and a queue, making it useful in various applications such as scheduling algorithms, sliding windows, and palindrome checking.

By understanding its operations and implementing it using appropriate data structures, you can leverage its power to solve specific problems efficiently.