Double Ended Queue Deque in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Double Ended Queue (Deque)?

A Double Ended Queue, or Deque, is a data structure where elements can be added or removed from both the front and the back ends.

beginner

Name two main operations that can be performed on both ends of a Deque.

Insertion (adding elements) and Deletion (removing elements) can be done at both the front and the rear ends of a Deque.

intermediate

In a Deque, what happens if you try to insert an element when it is full?

If the Deque is full, no more elements can be added until some are removed. This condition is called overflow.

beginner

How is a Deque different from a regular Queue?

A regular Queue allows insertion at the rear and deletion at the front only, while a Deque allows insertion and deletion at both front and rear ends.

intermediate

What is the typical use case for a Deque?

Deques are useful when you need to access or modify elements from both ends efficiently, such as in undo operations, palindromes checking, or sliding window problems.

Which operation is NOT possible in a Deque?

A Delete at rear

B Insert at middle

C Insert at front

D Delete at front

Deques allow insertion and deletion only at the front and rear ends, not in the middle.

What does 'overflow' mean in the context of a Deque?

A Deque is empty

B Deque has duplicate elements

C Deque has one element

D Deque is full

Overflow means the Deque is full and cannot accept new elements.

Which of these is a valid operation on a Deque?

A Insert at front and delete at rear

B Insert at middle

C Delete at middle

D Insert only at rear

Deques support insertion and deletion at both front and rear ends.

If you want to implement undo functionality, which data structure is most suitable?

A Deque

B Queue

C Stack

D Linked List

Deque allows adding and removing from both ends, useful for undo operations.

What is the output after these operations on an empty Deque: insertFront(10), insertRear(20), deleteFront(), insertFront(30)?

A 20 -> 30 -> null

B 10 -> 20 -> null

C 30 -> 20 -> null

D 30 -> 10 -> null

After insertFront(10) and insertRear(20), Deque is 10 -> 20. deleteFront() removes 10, leaving 20. insertFront(30) adds 30 at front, so Deque is 30 -> 20.

Explain how insertion and deletion work in a Double Ended Queue (Deque).

Think about adding or removing elements from both ends.

Describe a real-life example where a Deque would be useful and why.

Consider situations like undo actions or sliding windows.