What Is Dequeue in Data Structure?

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Scott Campbell

In data structures, dequeue (or double-ended queue) is an abstract data type that allows elements to be added or removed from both ends. It is similar to a queue and a stack combined, providing versatility in implementing various algorithms.

Operations on Dequeue

A dequeue supports the following operations:

  • Insertion at Front: Add an element to the front of the dequeue.
  • Insertion at Rear: Add an element to the rear of the dequeue.
  • Deletion from Front: Remove an element from the front of the dequeue.
  • Deletion from Rear: Remove an element from the rear of the dequeue.
  • Get Front: Get the value of the element at the front of the dequeue without removing it.
  • Get Rear: Get the value of the element at the rear of the dequeue without removing it.

The Underlying Structure

A dequeue can be implemented using various data structures, such as arrays or linked lists. The choice depends on specific requirements like efficiency in insertion, deletion, or random access.

In an array-based implementation, a circular array is often preferred as it allows efficient utilization of space. The front and rear pointers keep track of where elements are inserted and removed. When either pointer reaches either end of the array, they wrap around to utilize empty spaces if available, making it behave like a circular structure.

A linked list-based implementation uses nodes with pointers to maintain connections between elements. This approach allows dynamic allocation and deallocation of memory as elements are added or removed. The front and rear pointers point to the first and last nodes, respectively.

Use Cases

Dequeue finds applications in scenarios where elements need to be added or removed from both ends efficiently. Some common use cases include:

  • Deque: A double-ended queue is often used as a deque, allowing insertion and deletion at both ends in constant time, making it useful for algorithms like breadth-first search (BFS).
  • Sliding Window: Dequeue can be used to solve problems related to sliding windows, where a window of a fixed size moves through an array or sequence.
  • Infix to Postfix Conversion: Dequeue can be utilized in converting infix expressions to postfix notation, which simplifies evaluation.

Conclusion

A dequeue is a versatile data structure that allows efficient insertion and deletion at both ends. It combines the functionalities of a queue and a stack, making it useful in various algorithms and problem-solving scenarios. Whether implemented using arrays or linked lists, understanding the dequeue’s underlying structure and operations is crucial for effective utilization.

By incorporating dequeue into your programming toolkit, you can enhance your ability to solve problems efficiently and elegantly.

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