How is a circular queue different from a regular queue?

A circular queue is different from a regular queue as it treats the end and beginning as adjacent, allowing continuous rotation.

In a regular queue, also known as a linear queue, elements are added at the rear end and removed from the front end. This follows the First-In-First-Out (FIFO) principle. Once the queue is full, no more elements can be inserted, even if there is a space created by removing elements from the front. This is because the rear end has reached the end of the storage limit. This situation is known as "underflow".

On the other hand, a circular queue overcomes this limitation. In a circular queue, the last element points to the first element making a circular link. When we delete an element, the first position becomes free, but the rear doesn't change. So, when we insert a new element after the rear has reached the end of the queue, it gets stored at the first position of the queue, provided that space is not occupied. This makes a circular queue a better memory utilisation model than a regular queue.

In terms of implementation, a circular queue can be implemented using an array or a linked list. The condition for full queue changes in a circular queue. In a regular queue, if the rear has reached the end of the array, the queue is considered full. But in a circular queue, the queue is full when the next position of the rear is the front.

In summary, the main difference between a regular queue and a circular queue lies in their handling of the end of the queue. A regular queue considers the end of the queue as the end of its capacity, while a circular queue treats the end as adjacent to the beginning, allowing for continuous rotation and better space utilisation.