Circular Queue is a linear data structure that follows FIFO (first in first out) principle which means the item that is inserted first in the queue can be taken out first. It is also known as circular/ring buffer because the last position of the queue is circled back and connected with the first element thereby, forming a circular structure.
Sample Circular Queue
Abstaract Datatypes of Circular Queue:
The following are the operations that can be performed on a circular queue.
- enQueue()
- deQueue()
- front()
- rear()
1. enQueue():
enQueue is used to insert an item in the Queue. The new item will be inserted from the rear only if there is some space available in the queue. This operation take O(1) time.
2. deQueue():
deQueue is used for deleting an item from the queue. An item will be deleted from the front of a Queue only if there is atleast one item in the queue. It’s time complexity is constant i.e O(1).
If the Queue is empty it returns -1 in Array implementation and NULL in Linked List representation.
3. front():
front() is used to retrieve the starting element of the queue. It’s time complexity is constant.
If the Queue is empty it returns -1 in Array implementation and NULL in Linked List representation.
4. rear():
rear() is used to retrieve the last element of the queue. This operation takes O(1) time complexity.
If the Queue is empty it returns -1 in Array implementation and NULL in Linked List representation.
For more details about the operations and their implementation please refer to the article about “Circular Queue“
Applications of Circular Queue:
- In a page replacement algorithm, a circular list of pages is maintained and when a page needs to be replaced, the page in the front of the queue will be chosen.
- Computer systems supply a holding area for maintaining communication between two processes or two programs. This memory area is also known as a ring buffer.
- CPU Scheduling: In the Round-Robin scheduling algorithm, a circular queue is utilized to maintain processes that are in a ready state.
- Inter-process communication: Circular queue can be used for communication between different processes.
- Resource allocation: In operating systems, circular queue is used for managing resources.
Real-time Applications of Circular Queue:
- Months in a year: Jan –> Feb –> March –> and so on upto Dec–> Jan –> . . .
- Eating: Breakfast –> lunch –> snacks –> dinner –> breakfast –> and so on..
- Traffic Light is also a real-time application of circular queue.
- Clock is also a better example for the Circular Queue.
Advantages of Circular Queue:
- It provides a quick way to store FIFO data with a maximum size.
- Efficient utilization of the memory.
- Doesn’t use dynamic memory.
- Simple implementation.
- All operations occur in O(1) constant time.
Disadvantages of Circular Queue:
- In a circular queue, the number of elements you can store is only as much as the queue length, you have to know the maximum size beforehand.
- Some operations like deletion or insertion can be complex in circular queue.
- The implementation of some algorithms like priority queue can be difficult in circular queue.
- Circular queue has a fixed size, and when it is full, there is a risk of overflow if not managed properly.
- In the array implementation of Circular Queue, even though it has space to insert the elements it shows that the Circular Queue is full and gives the wrong size in some cases.