Queue (abstract Data Type) - Queue Implementation

Queue Implementation

Theoretically, one characteristic of a queue is that it does not have a specific capacity. Regardless of how many elements are already contained, a new element can always be added. It can also be empty, at which point removing an element will be impossible until a new element has been added again.

Fixed length arrays are limited in capacity, and inefficient because items need to be copied towards the head of the queue. However conceptually they are simple and work with early languages such as FORTRAN and BASIC which did not have pointers or objects. Most modern languages with objects or pointers can implement or come with libraries for dynamic lists. Such data structures may have not specified fixed capacity limit besides memory constraints. Queue overflow results from trying to add an element onto a full queue and queue underflow happens when trying to remove an element from an empty queue.

A bounded queue is a queue limited to a fixed number of items.

There are several efficient implementations of FIFO queues. An efficient implementation is one that can perform the operations—enqueuing and dequeuing—in O(1) time.

• Linked list
  • A doubly linked list has O(1) insertion and deletion at both ends, so is a natural choice for queues.
  • A regular singly linked list only has efficient insertion and deletion at one end. However, a small modification—keeping a pointer to the last node in addition to the first one—will enable it to implement an efficient queue.
• A deque implemented using a modified dynamic array