Design Circular Queue

Design Circular Queue is a Medium Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Design Patterns pattern, in the Design (General/Specific) subpattern.

Problem statement

Design your implementation of the circular queue. The circular queue is a linear data structure in which the operations are performed based on FIFO (First In First Out) principle, and the last position is connected back to the first position to make a circle. It is also called "Ring Buffer".

One of the benefits of the circular queue is that we can make use of the spaces in front of the queue. In a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. But using the circular queue, we can use the space to store new values.

Implement the MyCircularQueue class:

- MyCircularQueue(k) Initializes the object with the size of the queue to be k.

- int Front() Gets the front item from the queue. If the queue is empty, return -1.

- int Rear() Gets the last item from the queue. If the queue is empty, return -1.

- boolean enQueue(int value) Inserts an element into the circular queue. Return true if the operation is successful.

- boolean deQueue() Deletes an element from the circular queue. Return true if the operation is successful.

- boolean isEmpty() Checks whether the circular queue is empty or not.

- boolean isFull() Checks whether the circular queue is full or not.

You must solve the problem without using the built-in queue data structure in your programming language.

Example 1:

Input ["MyCircularQueue", "enQueue", "enQueue", "enQueue", "enQueue", "Rear", "isFull", "deQueue", "enQueue", "Rear"] [[3], [1], [2], [3], [4], [], [], [], [4], []] Output [null, true, true, true, false, 3, true, true, true, 4]

Explanation MyCircularQueue myCircularQueue = new MyCircularQueue(3); myCircularQueue.enQueue(1); // return True myCircularQueue.enQueue(2); // return True myCircularQueue.enQueue(3); // return True myCircularQueue.enQueue(4); // return False myCircularQueue.Rear(); // return 3 myCircularQueue.isFull(); // return True myCircularQueue.deQueue(); // return True myCircularQueue.enQueue(4); // return True myCircularQueue.Rear(); // return 4

Constraints:

- 1 <= k <= 1000

- 0 <= value <= 1000

- At most 3000 calls will be made to enQueue, deQueue, Front, Rear, isEmpty, and isFull.

Topics and companies

Topics: Array, Linked List, Design, Queue.

Reported in interviews at Facebook, Amazon, Microsoft, Rubrik, Oracle.

How to practise Design Circular Queue on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(1) for all operations (enQueue, deQueue, Front, Rear, isEmpty, isFull) because each operation involves only a constant number of arithmetic and array access operations. time and O(k), where k is the capacity of the queue, because we allocate a fixed-size buffer of size k to store the elements. space.

Open Design Circular Queue in the code editor, or read the Design Circular Queue editorial for a worked solution with its approach and complexity analysis.

Where Design Circular Queue sits in the DSA pattern sheet

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