Deque (Double-Ended Queue) – (Types, Examples, Characteristics, Applications)

A deque (short for Double-Ended Queue) is a linear data structure that allows the insertion and deletion of elements from both ends (front, and rear). Unlike a standard queue or stack, a deque is more versatile and can function as both (a stack or a queue) depending on how it is used.

Characteristics of Deque

  • Bidirectional Operations: Insertions and deletions can occur at both ends (front and rear).
  • Dynamic Size: Its size can grow or shrink dynamically as required.
  • No Fixed Restrictions: There are no restrictions on the number of operations at either end.

Types of Deques

There are two major types of deque

1. Input-Restricted Deque

This deque type restricts the insertion operation, but it is flexible when removing elements.

  • Insertion is allowed only at one end (either the front or rear).
  • Deletion is allowed from both ends (front and rear).

The following figure explains it in detail

Input Restricted Deque

2. Output-Restricted Deque

This deque type restricts the deletion operation, but it is flexible when adding elements.

  • Deletion is allowed only at one end (either the front or rear).
  • Insertion is allowed at both ends.
Output Restricted Deque

Applications of Deque

  • Sliding Window Problems: Deques are often used to find the maximum or minimum in a sliding window efficiently.
  • Palindrome Checking: Deques allow checking characters from both ends of a string.
  • Undo/Redo Functionality: Deques can store states for undo and redo operations in text editors.
  • Task Scheduling: Deques can be used to manage tasks that may need reordering or prioritization from both ends.
Important:
Queue can be Double-Ended Circular Queue which supports circular behavior with insertion and deletion from both ends.

Characteristics:

  • Memory efficiency is due to the circular structure.
  • Flexible operations due to double-ended access.