Which of the following is not the type of queue?

A queue is inherently a double-ended data structure.

It has two primary operations: enqueue (adding to the rear) and dequeue (removing from the front).

The term "single-ended queue" is a contradiction.

If it were single-ended, it would essentially be a stack, not a queue.

Therefore, among the given options, single-ended queue is not a valid type of queue.

The other options are valid queue types:

Priority queue: Elements have priorities, and the highest priority element is dequeued first.

Circular queue: The rear and front pointers wrap around to the beginning of the array when they reach the end.

Ordinary queue: The standard queue implementation with a front and rear pointer.